Display DNS probe results.

1. Modify the browser-side NetErrorTabHelper to send extra messages when it
   starts or declines to start a DNS probe.

2. Create a new error domain, "dnsprobe", with errors for "might run a DNS
   probe", "currently running a DNS probe", and all of the possible probe
   results.

3. Modify ChromeContentRendererClient to give the renderer-side NetErrorHelper
   a chance to choose the error strings before we call LocalizedError directly.

4. Catch DNS errors and provide the strings for the "might run a DNS probe"
   pseudo-error instead.

5. Add a function to neterror.html that lets us re-render the template with a
   new set of strings.

6. When we get a "probe started" message, replace the strings with those for
   the "currently running a DNS probe" pseudo-error.

7. When we get a "probe finished" message, replace the strings with those for
   the probe result.

8. When we get a "probe not run" message, replace the strings with those for
   the original error we received.

BUG=156415
TEST=DnsProbeBrowserTest

Review URL: https://chromiumcodereview.appspot.com/13270005

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@211950 0039d316-1c4b-4281-b951-d872f2087c98

32 files changed, 2535 insertions, 1326 deletions

diff --git a/chrome/app/generated_resources.grd b/chrome/app/generated_resources.grd
index fa61ffd..1ab910b 100644
--- a/chrome/app/generated_resources.grd
+++ b/chrome/app/generated_resources.grd
@@ -9711,6 +9711,11 @@ The following plug-in is unresponsive: <ph name="PLUGIN_NAME">$1
         <ph name="PRODUCT_NAME">&lt;span jscontent="productName"&gt;&lt;/span&gt;<ex>Google Chrome</ex></ph>
         won't use insecure connections in order to protect your privacy.
       </message>
+      <message name="IDS_ERRORPAGES_SUMMARY_DNS_PROBE_RUNNING" desc="Summary in the error page when DNS resolution failed and we are running a probe to figure out why.">
+        Unable to look up
+        <ph name="HOST_NAME">&lt;strong jscontent="hostName"&gt;&lt;/strong&gt;<ex>www.whatever.com</ex></ph>.
+        Trying to diagnose the problem...
+      </message>
 
       <message name="IDS_ERRORPAGES_ERROR_CODE" desc="At the bottom of error pages, a non-internationalized string or numeric code is displayed for debugging purposes">
         Error code: <ph name="ERROR_NAME">$1<ex>ERR_FILE_NOT_FOUND</ex></ph>
@@ -9782,6 +9787,9 @@ The following plug-in is unresponsive: <ph name="PLUGIN_NAME">$1
         Multiple distinct Location headers received.  This is disallowed to protect
         against HTTP response splitting attacks.
       </message>
+      <message name="IDS_ERRORPAGES_DETAILS_DNS_PROBE_RUNNING" desc="The error message displayed when we are waiting to see whether we will run a DNS probe.">
+        Waiting for DNS probe.
+      </message>
       <message name="IDS_ERRORPAGES_DETAILS_UNKNOWN" desc="The default error message displayed if we don't have a more specific error message.">
         Unknown error.
       </message>
diff --git a/chrome/browser/net/dns_probe_browsertest.cc b/chrome/browser/net/dns_probe_browsertest.cc
new file mode 100644
index 0000000..76d494a
--- /dev/null
+++ b/chrome/browser/net/dns_probe_browsertest.cc
@@ -0,0 +1,535 @@
+// Copyright 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/bind.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/message_loop.h"
+#include "base/path_service.h"
+#include "base/threading/thread_restrictions.h"
+#include "chrome/browser/browser_process.h"
+#include "chrome/browser/google/google_util.h"
+#include "chrome/browser/io_thread.h"
+#include "chrome/browser/net/dns_probe_test_util.h"
+#include "chrome/browser/net/net_error_tab_helper.h"
+#include "chrome/browser/net/url_request_mock_util.h"
+#include "chrome/browser/ui/browser.h"
+#include "chrome/browser/ui/tabs/tab_strip_model.h"
+#include "chrome/common/chrome_paths.h"
+#include "chrome/common/net/net_error_info.h"
+#include "chrome/test/base/in_process_browser_test.h"
+#include "chrome/test/base/ui_test_utils.h"
+#include "content/public/browser/browser_thread.h"
+#include "content/public/browser/web_contents.h"
+#include "content/public/test/browser_test_utils.h"
+#include "content/test/net/url_request_failed_job.h"
+#include "content/test/net/url_request_mock_http_job.h"
+#include "net/base/net_errors.h"
+#include "net/dns/dns_test_util.h"
+#include "net/url_request/url_request_filter.h"
+#include "net/url_request/url_request_job.h"
+#include "net/url_request/url_request_job_factory.h"
+
+using base::Bind;
+using base::Callback;
+using base::Closure;
+using base::ConstRef;
+using base::FilePath;
+using base::MessageLoop;
+using base::Unretained;
+using chrome_common_net::DnsProbeStatus;
+using content::BrowserThread;
+using content::URLRequestFailedJob;
+using content::URLRequestMockHTTPJob;
+using content::WebContents;
+using google_util::LinkDoctorBaseURL;
+using net::MockDnsClientRule;
+using net::NetworkDelegate;
+using net::URLRequest;
+using net::URLRequestFilter;
+using net::URLRequestJob;
+using net::URLRequestJobFactory;
+using ui_test_utils::NavigateToURL;
+using ui_test_utils::NavigateToURLBlockUntilNavigationsComplete;
+
+namespace chrome_browser_net {
+
+namespace {
+
+// Wraps DnsProbeService and delays callbacks until someone calls
+// CallDelayedCallbacks.  This allows the DnsProbeBrowserTest to enforce a
+// stricter ordering of events.
+class DelayingDnsProbeService : public DnsProbeService {
+ public:
+  DelayingDnsProbeService() {}
+
+  virtual ~DelayingDnsProbeService() {
+    EXPECT_TRUE(delayed_probes_.empty());
+  }
+
+  virtual void ProbeDns(const ProbeCallback& callback) OVERRIDE {
+    delayed_probes_.push_back(callback);
+  }
+
+  void StartDelayedProbes() {
+    CHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
+
+    std::vector<ProbeCallback> probes;
+    probes.swap(delayed_probes_);
+
+    for (std::vector<ProbeCallback>::const_iterator i = probes.begin();
+         i != probes.end(); ++i) {
+      DnsProbeService::ProbeDns(*i);
+    }
+  }
+
+  int delayed_probe_count() const {
+    CHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
+    return delayed_probes_.size();
+  }
+
+ private:
+  std::vector<ProbeCallback> delayed_probes_;
+};
+
+FilePath GetMockLinkDoctorFilePath() {
+  FilePath root_http;
+  PathService::Get(chrome::DIR_TEST_DATA, &root_http);
+  return root_http.AppendASCII("mock-link-doctor.html");
+}
+
+class BreakableLinkDoctorProtocolHandler
+    : public URLRequestJobFactory::ProtocolHandler {
+ public:
+  explicit BreakableLinkDoctorProtocolHandler(
+      const FilePath& mock_link_doctor_file_path)
+      : mock_link_doctor_file_path_(mock_link_doctor_file_path),
+        net_error_(net::OK) {}
+
+  virtual ~BreakableLinkDoctorProtocolHandler() {}
+
+  virtual URLRequestJob* MaybeCreateJob(
+      URLRequest* request, NetworkDelegate* network_delegate) const OVERRIDE {
+    if (net_error_ != net::OK) {
+      return new URLRequestFailedJob(request, network_delegate, net_error_);
+    } else {
+      return new URLRequestMockHTTPJob(
+          request, network_delegate, mock_link_doctor_file_path_);
+    }
+  }
+
+  void set_net_error(int net_error) { net_error_ = net_error; }
+
+ private:
+  const FilePath mock_link_doctor_file_path_;
+  int net_error_;
+};
+
+class DnsProbeBrowserTestIOThreadHelper {
+ public:
+  DnsProbeBrowserTestIOThreadHelper();
+
+  void SetUpOnIOThread(IOThread* io_thread);
+  void CleanUpOnIOThreadAndDeleteHelper();
+
+  void SetMockDnsClientRules(MockDnsClientRule::Result system_good_result,
+                             MockDnsClientRule::Result public_good_result);
+  void SetLinkDoctorNetError(int link_doctor_net_error);
+  void StartDelayedProbes(int expected_delayed_probe_count);
+
+ private:
+  IOThread* io_thread_;
+  DnsProbeService* original_dns_probe_service_;
+  DelayingDnsProbeService* delaying_dns_probe_service_;
+  BreakableLinkDoctorProtocolHandler* protocol_handler_;
+  FilePath mock_link_doctor_file_path_;
+};
+
+DnsProbeBrowserTestIOThreadHelper::DnsProbeBrowserTestIOThreadHelper()
+    : io_thread_(NULL),
+      original_dns_probe_service_(NULL),
+      delaying_dns_probe_service_(NULL),
+      protocol_handler_(NULL),
+      mock_link_doctor_file_path_(GetMockLinkDoctorFilePath()) {}
+
+void DnsProbeBrowserTestIOThreadHelper::SetUpOnIOThread(IOThread* io_thread) {
+  CHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
+  CHECK(io_thread);
+  CHECK(!io_thread_);
+  CHECK(!original_dns_probe_service_);
+  CHECK(!delaying_dns_probe_service_);
+  CHECK(!protocol_handler_);
+
+  io_thread_ = io_thread;
+
+  delaying_dns_probe_service_ = new DelayingDnsProbeService();
+
+  IOThread::Globals* globals = io_thread_->globals();
+  original_dns_probe_service_ = globals->dns_probe_service.release();
+  globals->dns_probe_service.reset(delaying_dns_probe_service_);
+
+  URLRequestFailedJob::AddUrlHandler();
+
+  scoped_ptr<URLRequestJobFactory::ProtocolHandler> protocol_handler(
+      new BreakableLinkDoctorProtocolHandler(mock_link_doctor_file_path_));
+  protocol_handler_ =
+      static_cast<BreakableLinkDoctorProtocolHandler*>(protocol_handler.get());
+  const GURL link_doctor_base_url = LinkDoctorBaseURL();
+  const std::string link_doctor_host = link_doctor_base_url.host();
+  URLRequestFilter::GetInstance()->AddHostnameProtocolHandler(
+      "http", link_doctor_host, protocol_handler.Pass());
+}
+
+void DnsProbeBrowserTestIOThreadHelper::CleanUpOnIOThreadAndDeleteHelper() {
+  CHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
+
+  URLRequestFilter::GetInstance()->ClearHandlers();
+
+  IOThread::Globals* globals = io_thread_->globals();
+  scoped_ptr<DnsProbeService> delaying_dns_probe_service(
+      globals->dns_probe_service.release());
+  globals->dns_probe_service.reset(original_dns_probe_service_);
+
+  CHECK_EQ(delaying_dns_probe_service_, delaying_dns_probe_service.get());
+
+  delete this;
+}
+
+void DnsProbeBrowserTestIOThreadHelper::SetMockDnsClientRules(
+    MockDnsClientRule::Result system_result,
+    MockDnsClientRule::Result public_result) {
+  CHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
+
+  DnsProbeService* service = io_thread_->globals()->dns_probe_service.get();
+  service->SetSystemClientForTesting(
+      CreateMockDnsClientForProbes(system_result));
+  service->SetPublicClientForTesting(
+      CreateMockDnsClientForProbes(public_result));
+}
+
+void DnsProbeBrowserTestIOThreadHelper::SetLinkDoctorNetError(
+    int link_doctor_net_error) {
+  CHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
+
+  protocol_handler_->set_net_error(link_doctor_net_error);
+}
+
+void DnsProbeBrowserTestIOThreadHelper::StartDelayedProbes(
+    int expected_delayed_probe_count) {
+  CHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
+
+  CHECK(delaying_dns_probe_service_);
+
+  int actual_delayed_probe_count =
+      delaying_dns_probe_service_->delayed_probe_count();
+  EXPECT_EQ(expected_delayed_probe_count, actual_delayed_probe_count);
+
+  delaying_dns_probe_service_->StartDelayedProbes();
+}
+
+class DnsProbeBrowserTest : public InProcessBrowserTest {
+ public:
+  DnsProbeBrowserTest();
+
+  virtual void SetUpOnMainThread() OVERRIDE;
+  virtual void CleanUpOnMainThread() OVERRIDE;
+
+ protected:
+  void SetLinkDoctorBroken(bool broken);
+  void SetMockDnsClientRules(MockDnsClientRule::Result system_result,
+                             MockDnsClientRule::Result public_result);
+  void NavigateToDnsError();
+  void NavigateToOtherError();
+
+  void StartDelayedProbes(int expected_delayed_probe_count);
+  DnsProbeStatus WaitForSentStatus();
+  int pending_status_count() const { return dns_probe_status_queue_.size(); }
+
+  std::string Title();
+  bool PageContains(const std::string& expected);
+
+ private:
+  void OnDnsProbeStatusSent(DnsProbeStatus dns_probe_status);
+
+  DnsProbeBrowserTestIOThreadHelper* helper_;
+
+  bool awaiting_dns_probe_status_;
+  // Queue of statuses received but not yet consumed by WaitForSentStatus().
+  std::list<DnsProbeStatus> dns_probe_status_queue_;
+};
+
+DnsProbeBrowserTest::DnsProbeBrowserTest()
+    : helper_(new DnsProbeBrowserTestIOThreadHelper()),
+      awaiting_dns_probe_status_(false) {
+}
+
+void DnsProbeBrowserTest::SetUpOnMainThread() {
+  NetErrorTabHelper::set_state_for_testing(
+      NetErrorTabHelper::TESTING_FORCE_ENABLED);
+
+  BrowserThread::PostTask(
+      BrowserThread::IO, FROM_HERE,
+      Bind(&DnsProbeBrowserTestIOThreadHelper::SetUpOnIOThread,
+           Unretained(helper_),
+           g_browser_process->io_thread()));
+
+  NetErrorTabHelper* tab_helper = NetErrorTabHelper::FromWebContents(
+      browser()->tab_strip_model()->GetActiveWebContents());
+  tab_helper->set_dns_probe_status_snoop_callback_for_testing(Bind(
+      &DnsProbeBrowserTest::OnDnsProbeStatusSent,
+      Unretained(this)));
+}
+
+void DnsProbeBrowserTest::CleanUpOnMainThread() {
+  BrowserThread::PostTask(
+      BrowserThread::IO, FROM_HERE,
+      Bind(&DnsProbeBrowserTestIOThreadHelper::CleanUpOnIOThreadAndDeleteHelper,
+           Unretained(helper_)));
+
+  NetErrorTabHelper::set_state_for_testing(
+      NetErrorTabHelper::TESTING_DEFAULT);
+}
+
+void DnsProbeBrowserTest::SetLinkDoctorBroken(bool broken) {
+  int net_error = broken ? net::ERR_NAME_NOT_RESOLVED : net::OK;
+
+  BrowserThread::PostTask(
+      BrowserThread::IO, FROM_HERE,
+      Bind(&DnsProbeBrowserTestIOThreadHelper::SetLinkDoctorNetError,
+           Unretained(helper_),
+           net_error));
+}
+
+// These two functions wait for two navigations because Link Doctor loads two
+// pages: a blank page, so the user stops seeing the previous page, and then
+// either the Link Doctor page or a regular error page.  We want to wait for
+// the error page, so we wait for both loads to finish.
+
+void DnsProbeBrowserTest::NavigateToDnsError() {
+  NavigateToURLBlockUntilNavigationsComplete(
+      browser(),
+      URLRequestFailedJob::GetMockHttpUrl(net::ERR_NAME_NOT_RESOLVED),
+      2);
+}
+
+void DnsProbeBrowserTest::NavigateToOtherError() {
+  NavigateToURLBlockUntilNavigationsComplete(
+      browser(),
+      URLRequestFailedJob::GetMockHttpUrl(net::ERR_CONNECTION_REFUSED),
+      2);
+}
+
+void DnsProbeBrowserTest::SetMockDnsClientRules(
+    MockDnsClientRule::Result system_result,
+    MockDnsClientRule::Result public_result) {
+  BrowserThread::PostTask(
+      BrowserThread::IO, FROM_HERE,
+      Bind(&DnsProbeBrowserTestIOThreadHelper::SetMockDnsClientRules,
+           Unretained(helper_),
+           system_result,
+           public_result));
+}
+
+void DnsProbeBrowserTest::StartDelayedProbes(
+    int expected_delayed_probe_count) {
+  BrowserThread::PostTask(
+      BrowserThread::IO, FROM_HERE,
+      Bind(&DnsProbeBrowserTestIOThreadHelper::StartDelayedProbes,
+           Unretained(helper_),
+           expected_delayed_probe_count));
+}
+
+DnsProbeStatus DnsProbeBrowserTest::WaitForSentStatus() {
+  CHECK(!awaiting_dns_probe_status_);
+  while (dns_probe_status_queue_.empty()) {
+    awaiting_dns_probe_status_ = true;
+    MessageLoop::current()->Run();
+    awaiting_dns_probe_status_ = false;
+  }
+
+  CHECK(!dns_probe_status_queue_.empty());
+  DnsProbeStatus status = dns_probe_status_queue_.front();
+  dns_probe_status_queue_.pop_front();
+  return status;
+}
+
+// Check title by roundtripping to renderer, to make sure any probe results
+// sent before this have been applied.
+std::string DnsProbeBrowserTest::Title() {
+  std::string title;
+
+  WebContents* contents =
+      browser()->tab_strip_model()->GetActiveWebContents();
+
+  bool rv = content::ExecuteScriptAndExtractString(
+      contents,
+      "domAutomationController.send(document.title);",
+      &title);
+  if (!rv)
+    return "";
+
+  return title;
+}
+
+// Check text by roundtripping to renderer, to make sure any probe results
+// sent before this have been applied.
+bool DnsProbeBrowserTest::PageContains(const std::string& expected) {
+  std::string text_content;
+
+  bool rv = content::ExecuteScriptAndExtractString(
+      browser()->tab_strip_model()->GetActiveWebContents(),
+      "domAutomationController.send(document.body.textContent);",
+      &text_content);
+  if (!rv)
+    return false;
+
+  return text_content.find(expected) != std::string::npos;
+}
+
+void DnsProbeBrowserTest::OnDnsProbeStatusSent(
+    DnsProbeStatus dns_probe_status) {
+  dns_probe_status_queue_.push_back(dns_probe_status);
+  if (awaiting_dns_probe_status_)
+    MessageLoop::current()->Quit();
+}
+
+// Make sure probes don't break non-DNS error pages when Link Doctor loads.
+IN_PROC_BROWSER_TEST_F(DnsProbeBrowserTest, OtherErrorWithWorkingLinkDoctor) {
+  SetLinkDoctorBroken(false);
+
+  NavigateToOtherError();
+  EXPECT_EQ("Mock Link Doctor", Title());
+
+  EXPECT_EQ(0, pending_status_count());
+}
+
+// Make sure probes don't break non-DNS error pages when Link Doctor doesn't
+// load.
+IN_PROC_BROWSER_TEST_F(DnsProbeBrowserTest, OtherErrorWithBrokenLinkDoctor) {
+  SetLinkDoctorBroken(true);
+
+  NavigateToOtherError();
+  EXPECT_TRUE(PageContains("CONNECTION_REFUSED"));
+
+  EXPECT_EQ(0, pending_status_count());
+}
+
+// Make sure probes don't break DNS error pages when Link doctor loads.
+IN_PROC_BROWSER_TEST_F(DnsProbeBrowserTest,
+    NxdomainProbeResultWithWorkingLinkDoctor) {
+  SetLinkDoctorBroken(false);
+  SetMockDnsClientRules(MockDnsClientRule::OK, MockDnsClientRule::OK);
+
+  NavigateToDnsError();
+  EXPECT_EQ("Mock Link Doctor", Title());
+
+  EXPECT_EQ(chrome_common_net::DNS_PROBE_STARTED, WaitForSentStatus());
+  EXPECT_EQ(chrome_common_net::DNS_PROBE_STARTED, WaitForSentStatus());
+  EXPECT_EQ(0, pending_status_count());
+  EXPECT_EQ("Mock Link Doctor", Title());
+
+  StartDelayedProbes(1);
+
+  EXPECT_EQ(chrome_common_net::DNS_PROBE_FINISHED_NXDOMAIN,
+            WaitForSentStatus());
+  EXPECT_EQ(0, pending_status_count());
+  EXPECT_EQ("Mock Link Doctor", Title());
+}
+
+// Make sure probes update DNS error page properly when they're supposed to.
+IN_PROC_BROWSER_TEST_F(DnsProbeBrowserTest,
+    NoInternetProbeResultWithBrokenLinkDoctor) {
+  SetLinkDoctorBroken(true);
+  SetMockDnsClientRules(MockDnsClientRule::TIMEOUT,
+                        MockDnsClientRule::TIMEOUT);
+
+  NavigateToDnsError();
+
+  EXPECT_EQ(chrome_common_net::DNS_PROBE_STARTED, WaitForSentStatus());
+  EXPECT_EQ(chrome_common_net::DNS_PROBE_STARTED, WaitForSentStatus());
+
+  // PageContains runs the RunLoop, so make sure nothing hairy happens.
+  EXPECT_EQ(0, pending_status_count());
+  EXPECT_TRUE(PageContains("DNS_PROBE_STARTED"));
+  EXPECT_EQ(0, pending_status_count());
+
+  StartDelayedProbes(1);
+
+  EXPECT_EQ(chrome_common_net::DNS_PROBE_FINISHED_NO_INTERNET,
+            WaitForSentStatus());
+
+  // PageContains runs the RunLoop, so make sure nothing hairy happens.
+  EXPECT_EQ(0, pending_status_count());
+  EXPECT_TRUE(PageContains("DNS_PROBE_FINISHED_NO_INTERNET"));
+  EXPECT_EQ(0, pending_status_count());
+}
+
+// Double-check to make sure sync failures don't explode.
+IN_PROC_BROWSER_TEST_F(DnsProbeBrowserTest, SyncFailureWithBrokenLinkDoctor) {
+  SetLinkDoctorBroken(true);
+  SetMockDnsClientRules(MockDnsClientRule::FAIL_SYNC,
+                        MockDnsClientRule::FAIL_SYNC);
+
+  NavigateToDnsError();
+
+  EXPECT_EQ(chrome_common_net::DNS_PROBE_STARTED, WaitForSentStatus());
+  EXPECT_EQ(chrome_common_net::DNS_PROBE_STARTED, WaitForSentStatus());
+
+  // PageContains runs the RunLoop, so make sure nothing hairy happens.
+  EXPECT_EQ(0, pending_status_count());
+  EXPECT_TRUE(PageContains("DNS_PROBE_STARTED"));
+  EXPECT_EQ(0, pending_status_count());
+
+  StartDelayedProbes(1);
+
+  EXPECT_EQ(chrome_common_net::DNS_PROBE_FINISHED_INCONCLUSIVE,
+            WaitForSentStatus());
+
+  // PageContains runs the RunLoop, so make sure nothing hairy happens.
+  EXPECT_EQ(0, pending_status_count());
+  EXPECT_TRUE(PageContains("NAME_NOT_RESOLVED"));
+  EXPECT_EQ(0, pending_status_count());
+}
+
+// Make sure probes don't run for subframe DNS errors.
+IN_PROC_BROWSER_TEST_F(DnsProbeBrowserTest, NoProbeInSubframe) {
+  SetLinkDoctorBroken(false);
+
+  const FilePath::CharType kIframeDnsErrorHtmlName[] =
+      FILE_PATH_LITERAL("iframe_dns_error.html");
+
+  NavigateToURL(
+      browser(),
+      URLRequestMockHTTPJob::GetMockUrl(FilePath(kIframeDnsErrorHtmlName)));
+
+  // By the time NavigateToURL returns, the browser will have seen the failed
+  // provisional load.  If a probe was started (or considered but not run),
+  // then the NetErrorTabHelper would have sent a NetErrorInfo message.  Thus,
+  // if one hasn't been sent by now, the NetErrorTabHelper has not (and won't)
+  // start a probe for this DNS error.
+  EXPECT_EQ(0, pending_status_count());
+}
+
+// Make sure browser sends NOT_RUN properly when probes are disabled.
+IN_PROC_BROWSER_TEST_F(DnsProbeBrowserTest, ProbesDisabled) {
+  NetErrorTabHelper::set_state_for_testing(
+      NetErrorTabHelper::TESTING_FORCE_DISABLED);
+
+  SetLinkDoctorBroken(true);
+  SetMockDnsClientRules(MockDnsClientRule::TIMEOUT,
+                        MockDnsClientRule::TIMEOUT);
+
+  NavigateToDnsError();
+
+  EXPECT_EQ(chrome_common_net::DNS_PROBE_NOT_RUN, WaitForSentStatus());
+  EXPECT_EQ(chrome_common_net::DNS_PROBE_NOT_RUN, WaitForSentStatus());
+
+  // PageContains runs the RunLoop, so make sure nothing hairy happens.
+  EXPECT_EQ(0, pending_status_count());
+  EXPECT_TRUE(PageContains("NAME_NOT_RESOLVED"));
+  EXPECT_EQ(0, pending_status_count());
+}
+
+}  // namespace
+
+}  // namespace chrome_browser_net
diff --git a/chrome/browser/net/dns_probe_job.cc b/chrome/browser/net/dns_probe_job.cc
deleted file mode 100644
index f51f450..0000000
--- a/chrome/browser/net/dns_probe_job.cc
+++ /dev/null
@@ -1,236 +0,0 @@
-// Copyright (c) 2012 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#include "chrome/browser/net/dns_probe_job.h"
-
-#include "base/compiler_specific.h"
-#include "base/memory/scoped_ptr.h"
-#include "base/memory/weak_ptr.h"
-#include "base/message_loop.h"
-#include "base/time/time.h"
-#include "net/base/address_list.h"
-#include "net/base/net_errors.h"
-#include "net/base/net_log.h"
-#include "net/dns/dns_client.h"
-#include "net/dns/dns_protocol.h"
-#include "net/dns/dns_response.h"
-#include "net/dns/dns_transaction.h"
-
-using base::TimeDelta;
-using net::AddressList;
-using net::BoundNetLog;
-using net::DnsClient;
-using net::DnsResponse;
-using net::DnsTransaction;
-using net::NetLog;
-
-namespace chrome_browser_net {
-
-namespace {
-
-// Returns true if the given net_error indicates that we received a response
-// from the DNS server containing an error, or false if the given net_error
-// indicates that we never received a response.
-bool DidReceiveDnsResponse(int net_error) {
-  switch (net_error) {
-  case net::ERR_NAME_NOT_RESOLVED:  // NXDOMAIN maps to this.
-  case net::ERR_DNS_MALFORMED_RESPONSE:
-  case net::ERR_DNS_SERVER_REQUIRES_TCP:
-  case net::ERR_DNS_SERVER_FAILED:
-  case net::ERR_DNS_SORT_ERROR:  // Can only happen if the server responds.
-    return true;
-  default:
-    return false;
-  }
-}
-
-class DnsProbeJobImpl : public DnsProbeJob {
- public:
-  DnsProbeJobImpl(scoped_ptr<DnsClient> dns_client,
-                  const DnsProbeJob::CallbackType& callback,
-                  NetLog* net_log);
-  virtual ~DnsProbeJobImpl();
-
- private:
-  enum QueryResult {
-    QUERY_UNKNOWN,
-    QUERY_CORRECT,
-    QUERY_INCORRECT,
-    QUERY_DNS_ERROR,
-    QUERY_NET_ERROR,
-  };
-
-  void Start();
-
-  scoped_ptr<DnsTransaction> CreateTransaction(
-      const std::string& hostname);
-  void StartTransaction(DnsTransaction* transaction);
-  // Checks that |net_error| is OK, |response| parses, and has at least one
-  // address.
-  QueryResult EvaluateGoodResponse(int net_error, const DnsResponse* response);
-  // Checks that |net_error| is OK, |response| parses but has no addresses.
-  QueryResult EvaluateBadResponse(int net_error, const DnsResponse* response);
-  DnsProbeJob::Result EvaluateQueryResults();
-  void OnTransactionComplete(DnsTransaction* transaction,
-                             int net_error,
-                             const DnsResponse* response);
-
-  BoundNetLog bound_net_log_;
-  scoped_ptr<DnsClient> dns_client_;
-  const DnsProbeJob::CallbackType callback_;
-  scoped_ptr<DnsTransaction> good_transaction_;
-  scoped_ptr<DnsTransaction> bad_transaction_;
-  bool good_running_;
-  bool bad_running_;
-  QueryResult good_result_;
-  QueryResult bad_result_;
-  base::WeakPtrFactory<DnsProbeJobImpl> weak_factory_;
-
-  DISALLOW_COPY_AND_ASSIGN(DnsProbeJobImpl);
-};
-
-DnsProbeJobImpl::DnsProbeJobImpl(scoped_ptr<DnsClient> dns_client,
-                                 const DnsProbeJob::CallbackType& callback,
-                                 NetLog* net_log)
-    : bound_net_log_(
-          BoundNetLog::Make(net_log, NetLog::SOURCE_DNS_PROBER)),
-      dns_client_(dns_client.Pass()),
-      callback_(callback),
-      good_running_(false),
-      bad_running_(false),
-      good_result_(QUERY_UNKNOWN),
-      bad_result_(QUERY_UNKNOWN),
-      weak_factory_(this) {
-  DCHECK(dns_client_.get());
-  DCHECK(dns_client_->GetConfig());
-
-  base::MessageLoop::current()->PostTask(
-      FROM_HERE,
-      base::Bind(&DnsProbeJobImpl::Start,
-                 weak_factory_.GetWeakPtr()));
-}
-
-DnsProbeJobImpl::~DnsProbeJobImpl() {
-}
-
-void DnsProbeJobImpl::Start() {
-  // TODO(ttuttle): Pick a good random hostname for the bad case.
-  //                Consider running transactions in series?
-  good_transaction_ = CreateTransaction("google.com");
-  bad_transaction_ = CreateTransaction("thishostname.doesnotresolve");
-
-  // StartTransaction may call the callback synchrononously, so set these
-  // before we call it.
-  good_running_ = true;
-  bad_running_ = true;
-
-  // TODO(ttuttle): Log probe started.
-
-  StartTransaction(good_transaction_.get());
-  StartTransaction(bad_transaction_.get());
-}
-
-scoped_ptr<DnsTransaction> DnsProbeJobImpl::CreateTransaction(
-    const std::string& hostname) {
-  return dns_client_->GetTransactionFactory()->CreateTransaction(
-      hostname,
-      net::dns_protocol::kTypeA,
-      base::Bind(&DnsProbeJobImpl::OnTransactionComplete,
-                 base::Unretained(this)),
-      bound_net_log_);
-}
-
-void DnsProbeJobImpl::StartTransaction(DnsTransaction* transaction) {
-  int rv = transaction->Start();
-  if (rv != net::ERR_IO_PENDING) {
-    // TODO(ttuttle): Make sure this counts as unreachable, not error.
-    OnTransactionComplete(transaction, rv, NULL);
-  }
-
-  // TODO(ttuttle): Log transaction started.
-}
-
-DnsProbeJobImpl::QueryResult DnsProbeJobImpl::EvaluateGoodResponse(
-    int net_error,
-    const DnsResponse* response) {
-  if (net_error != net::OK)
-    return DidReceiveDnsResponse(net_error) ? QUERY_DNS_ERROR : QUERY_NET_ERROR;
-
-  AddressList addr_list;
-  TimeDelta ttl;
-  DnsResponse::Result result = response->ParseToAddressList(&addr_list, &ttl);
-
-  if (result != DnsResponse::DNS_PARSE_OK)
-    return QUERY_DNS_ERROR;
-
-  if (addr_list.empty())
-    return QUERY_INCORRECT;
-
-  return QUERY_CORRECT;
-}
-
-DnsProbeJobImpl::QueryResult DnsProbeJobImpl::EvaluateBadResponse(
-    int net_error,
-    const DnsResponse* response) {
-  if (net_error == net::ERR_NAME_NOT_RESOLVED)  // NXDOMAIN maps to this
-    return QUERY_CORRECT;
-
-  if (net_error != net::OK)
-    return DidReceiveDnsResponse(net_error) ? QUERY_DNS_ERROR : QUERY_NET_ERROR;
-
-  return QUERY_INCORRECT;
-}
-
-DnsProbeJob::Result DnsProbeJobImpl::EvaluateQueryResults() {
-  if (good_result_ == QUERY_NET_ERROR || bad_result_ == QUERY_NET_ERROR)
-    return SERVERS_UNREACHABLE;
-
-  if (good_result_ == QUERY_DNS_ERROR || bad_result_ == QUERY_DNS_ERROR)
-    return SERVERS_FAILING;
-
-  // Ignore incorrect responses to known-bad query to avoid flagging domain
-  // helpers.
-  if (good_result_ == QUERY_INCORRECT)
-    return SERVERS_INCORRECT;
-
-  return SERVERS_CORRECT;
-}
-
-void DnsProbeJobImpl::OnTransactionComplete(DnsTransaction* transaction,
-                                            int net_error,
-                                            const DnsResponse* response) {
-  if (transaction == good_transaction_.get()) {
-    DCHECK(good_running_);
-    DCHECK_EQ(QUERY_UNKNOWN, good_result_);
-    good_result_ = EvaluateGoodResponse(net_error, response);
-    good_running_ = false;
-  } else if (transaction == bad_transaction_.get()) {
-    DCHECK(bad_running_);
-    DCHECK_EQ(QUERY_UNKNOWN, bad_result_);
-    bad_result_ = EvaluateBadResponse(net_error, response);
-    bad_running_ = false;
-  } else {
-    NOTREACHED();
-    return;
-  }
-
-  if (good_running_ || bad_running_)
-    return;
-
-  callback_.Run(this, EvaluateQueryResults());
-
-  // TODO(ttuttle): Log probe finished.
-}
-
-}  // namespace
-
-scoped_ptr<DnsProbeJob> DnsProbeJob::CreateJob(
-    scoped_ptr<DnsClient> dns_client,
-    const CallbackType& callback,
-    NetLog* net_log) {
-  return scoped_ptr<DnsProbeJob>(
-      new DnsProbeJobImpl(dns_client.Pass(), callback, net_log));
-}
-
-}  // namespace chrome_browser_net
diff --git a/chrome/browser/net/dns_probe_job.h b/chrome/browser/net/dns_probe_job.h
deleted file mode 100644
index 6572de1..0000000
--- a/chrome/browser/net/dns_probe_job.h
+++ /dev/null
@@ -1,55 +0,0 @@
-// Copyright (c) 2012 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#ifndef CHROME_BROWSER_NET_DNS_PROBE_JOB_H_
-#define CHROME_BROWSER_NET_DNS_PROBE_JOB_H_
-
-#include "base/basictypes.h"
-#include "base/bind.h"
-#include "base/memory/scoped_ptr.h"
-
-namespace net {
-class DnsClient;
-class NetLog;
-}
-
-namespace chrome_browser_net {
-
-// A job to probe the health of a DNS configuration.
-class DnsProbeJob {
- public:
-  enum Result {
-    SERVERS_UNKNOWN,
-    SERVERS_CORRECT,  // Server responds with correct answers.
-    SERVERS_INCORRECT,  // Server responds with success but incorrect answer.
-    // TODO(ttuttle): Do we want an "unreliable" result, for e.g. servers that
-    // lie about NXDOMAIN?
-    SERVERS_FAILING,  // Server responds with errors.
-    SERVERS_UNREACHABLE,  // Server doesn't respond (or never got our packets)
-    MAX_RESULT
-  };
-  typedef base::Callback<void(DnsProbeJob* job, Result result)> CallbackType;
-
-  virtual ~DnsProbeJob() { }
-
-  // Creates and starts a probe job.
-  //
-  // |dns_client| should be a DnsClient with the DnsConfig already set.
-  // |callback| will be called when the probe finishes, which may happen
-  // before the constructor returns (for example, if we can't create the DNS
-  // transactions).
-  static scoped_ptr<DnsProbeJob> CreateJob(
-      scoped_ptr<net::DnsClient> dns_client,
-      const CallbackType& callback,
-      net::NetLog* net_log);
-
- protected:
-  DnsProbeJob() { }
-
-  DISALLOW_COPY_AND_ASSIGN(DnsProbeJob);
-};
-
-}  // namespace chrome_browser_net
-
-#endif  // CHROME_BROWSER_NET_DNS_PROBE_JOB_H_
diff --git a/chrome/browser/net/dns_probe_job_unittest.cc b/chrome/browser/net/dns_probe_job_unittest.cc
deleted file mode 100644
index d1779b1..0000000
--- a/chrome/browser/net/dns_probe_job_unittest.cc
+++ /dev/null
@@ -1,127 +0,0 @@
-// Copyright (c) 2012 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#include "chrome/browser/net/dns_probe_job.h"
-
-#include "base/basictypes.h"
-#include "base/message_loop.h"
-#include "base/run_loop.h"
-#include "net/base/net_log.h"
-#include "net/dns/dns_client.h"
-#include "net/dns/dns_config_service.h"
-#include "net/dns/dns_protocol.h"
-#include "net/dns/dns_test_util.h"
-#include "testing/gtest/include/gtest/gtest.h"
-
-using net::DnsClient;
-using net::DnsConfig;
-using net::IPAddressNumber;
-using net::IPEndPoint;
-using net::ParseIPLiteralToNumber;
-using net::MockDnsClientRule;
-using net::MockDnsClientRuleList;
-using net::NetLog;
-
-namespace chrome_browser_net {
-
-namespace {
-
-class DnsProbeJobTest : public testing::Test {
- public:
-  void RunProbe(MockDnsClientRule::Result expected_good_result,
-                MockDnsClientRule::Result expected_bad_result);
-
- protected:
-  void OnProbeFinished(DnsProbeJob* job, DnsProbeJob::Result result);
-
-  bool callback_called_;
-  DnsProbeJob::Result callback_result_;
-};
-
-// Runs a probe and waits for the callback.  |good_result| and |bad_result|
-// are the result of the good and bad transactions that the DnsProbeJob will
-// receive.
-void DnsProbeJobTest::RunProbe(MockDnsClientRule::Result good_result,
-                               MockDnsClientRule::Result bad_result) {
-  DnsConfig config;
-  config.nameservers.clear();
-  IPAddressNumber dns_ip;
-  ParseIPLiteralToNumber("192.168.1.1", &dns_ip);
-  const uint16 kDnsPort = net::dns_protocol::kDefaultPort;
-  config.nameservers.push_back(IPEndPoint(dns_ip, kDnsPort));
-
-  const uint16 kTypeA = net::dns_protocol::kTypeA;
-  MockDnsClientRuleList rules;
-  rules.push_back(MockDnsClientRule("google.com", kTypeA, good_result));
-  rules.push_back(MockDnsClientRule(std::string(), kTypeA, bad_result));
-
-  scoped_ptr<DnsClient> dns_client = CreateMockDnsClient(config, rules);
-  dns_client->SetConfig(config);
-
-  NetLog* net_log = NULL;
-  DnsProbeJob::CallbackType callback = base::Bind(
-      &DnsProbeJobTest::OnProbeFinished,
-      base::Unretained(this));
-
-  // Need to set these before creating job, because it can call the callback
-  // synchronously in the constructor if both transactions fail to start.
-  callback_called_ = false;
-  callback_result_ = DnsProbeJob::SERVERS_UNKNOWN;
-
-  // DnsProbeJob needs somewhere to post the callback.
-  scoped_ptr<base::MessageLoop> message_loop_(new base::MessageLoopForIO());
-
-  scoped_ptr<DnsProbeJob> job(
-      DnsProbeJob::CreateJob(dns_client.Pass(), callback, net_log));
-
-  // Force callback to run.
-  base::RunLoop run_loop;
-  run_loop.RunUntilIdle();
-}
-
-void DnsProbeJobTest::OnProbeFinished(DnsProbeJob* job,
-                                      DnsProbeJob::Result result) {
-  EXPECT_FALSE(callback_called_);
-
-  callback_called_ = true;
-  callback_result_ = result;
-}
-
-struct TestCase {
-  MockDnsClientRule::Result good_result;
-  MockDnsClientRule::Result bad_result;
-  DnsProbeJob::Result expected_probe_result;
-};
-
-TEST_F(DnsProbeJobTest, Test) {
-  static const TestCase kTestCases[] = {
-    { MockDnsClientRule::OK,
-      MockDnsClientRule::EMPTY,
-      DnsProbeJob::SERVERS_CORRECT },
-    { MockDnsClientRule::EMPTY,
-      MockDnsClientRule::EMPTY,
-      DnsProbeJob::SERVERS_INCORRECT },
-    // TODO(ttuttle): Test that triggers QUERY_DNS_ERROR.
-    //                (Need to add another mock behavior to MockDnsClient.)
-    { MockDnsClientRule::FAIL_ASYNC,
-      MockDnsClientRule::FAIL_ASYNC,
-      DnsProbeJob::SERVERS_FAILING },
-    { MockDnsClientRule::FAIL_SYNC,
-      MockDnsClientRule::FAIL_SYNC,
-      DnsProbeJob::SERVERS_FAILING },
-    { MockDnsClientRule::TIMEOUT,
-      MockDnsClientRule::TIMEOUT,
-      DnsProbeJob::SERVERS_UNREACHABLE },
-  };
-  for (size_t i = 0; i < arraysize(kTestCases); i++) {
-    const TestCase* test_case = &kTestCases[i];
-    RunProbe(test_case->good_result, test_case->bad_result);
-    EXPECT_TRUE(callback_called_);
-    EXPECT_EQ(test_case->expected_probe_result, callback_result_);
-  }
-}
-
-}  // namespace
-
-}  // namespace chrome_browser_net
diff --git a/chrome/browser/net/dns_probe_runner.cc b/chrome/browser/net/dns_probe_runner.cc
new file mode 100644
index 0000000..d2b3a5d7
--- /dev/null
+++ b/chrome/browser/net/dns_probe_runner.cc
@@ -0,0 +1,143 @@
+// Copyright 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "chrome/browser/net/dns_probe_runner.h"
+
+#include "base/bind.h"
+#include "content/public/browser/browser_thread.h"
+#include "net/base/address_list.h"
+#include "net/base/ip_endpoint.h"
+#include "net/base/net_errors.h"
+#include "net/base/net_log.h"
+#include "net/base/net_util.h"
+#include "net/base/network_change_notifier.h"
+#include "net/dns/dns_client.h"
+#include "net/dns/dns_protocol.h"
+#include "net/dns/dns_response.h"
+#include "net/dns/dns_transaction.h"
+
+using base::TimeDelta;
+using content::BrowserThread;
+using net::AddressList;
+using net::BoundNetLog;
+using net::DnsClient;
+using net::DnsResponse;
+using net::DnsTransaction;
+using net::IPAddressNumber;
+using net::IPEndPoint;
+using net::NetLog;
+using net::NetworkChangeNotifier;
+using net::ParseIPLiteralToNumber;
+
+namespace chrome_browser_net {
+
+const char* DnsProbeRunner::kKnownGoodHostname = "google.com";
+
+namespace {
+
+DnsProbeRunner::Result EvaluateResponse(
+    int net_error,
+    const DnsResponse* response) {
+  switch (net_error) {
+    case net::OK:
+      break;
+
+    // ERR_NAME_NOT_RESOLVED maps to NXDOMAIN, which means the server is working
+    // but gave us a wrong answer.
+    case net::ERR_NAME_NOT_RESOLVED:
+      return DnsProbeRunner::INCORRECT;
+
+    // These results mean we heard *something* from the DNS server, but it was
+    // unsuccessful (SERVFAIL) or malformed.
+    case net::ERR_DNS_MALFORMED_RESPONSE:
+    case net::ERR_DNS_SERVER_REQUIRES_TCP:  // Shouldn't happen; DnsTransaction
+                                            // will retry with TCP.
+    case net::ERR_DNS_SERVER_FAILED:
+    case net::ERR_DNS_SORT_ERROR:  // Can only happen if the server responds.
+      return DnsProbeRunner::FAILING;
+
+    // Any other error means we never reached the DNS server in the first place.
+    case net::ERR_DNS_TIMED_OUT:
+    default:
+      // Something else happened, probably at a network level.
+      return DnsProbeRunner::UNREACHABLE;
+  }
+
+  AddressList addr_list;
+  TimeDelta ttl;
+  DnsResponse::Result result = response->ParseToAddressList(&addr_list, &ttl);
+
+  if (result != DnsResponse::DNS_PARSE_OK) {
+    return DnsProbeRunner::FAILING;
+  }
+
+  if (addr_list.empty()) {
+    return DnsProbeRunner::INCORRECT;
+  }
+
+  return DnsProbeRunner::CORRECT;
+}
+
+}  // namespace
+
+DnsProbeRunner::DnsProbeRunner() : weak_factory_(this), result_(UNKNOWN) {}
+
+DnsProbeRunner::~DnsProbeRunner() {}
+
+void DnsProbeRunner::SetClient(scoped_ptr<net::DnsClient> client) {
+  client_ = client.Pass();
+}
+
+void DnsProbeRunner::RunProbe(const base::Closure& callback) {
+  DCHECK(!callback.is_null());
+  DCHECK(client_.get());
+  DCHECK(callback_.is_null());
+  DCHECK(!transaction_.get());
+
+  callback_ = callback;
+  transaction_ = client_->GetTransactionFactory()->CreateTransaction(
+      kKnownGoodHostname,
+      net::dns_protocol::kTypeA,
+      base::Bind(&DnsProbeRunner::OnTransactionComplete,
+                 weak_factory_.GetWeakPtr()),
+      BoundNetLog());
+
+  int rv = transaction_->Start();
+  if (rv != net::ERR_IO_PENDING)
+    OnTransactionComplete(transaction_.get(), rv, NULL);
+}
+
+bool DnsProbeRunner::IsRunning() const {
+  return !callback_.is_null();
+}
+
+void DnsProbeRunner::OnTransactionComplete(
+    DnsTransaction* transaction,
+    int net_error,
+    const DnsResponse* response) {
+  DCHECK(!callback_.is_null());
+  DCHECK(transaction_.get());
+  DCHECK_EQ(transaction_.get(), transaction);
+
+  result_ = EvaluateResponse(net_error, response);
+  transaction_.reset();
+
+  BrowserThread::PostTask(
+      BrowserThread::IO,
+      FROM_HERE,
+      base::Bind(&DnsProbeRunner::CallCallback,
+                 weak_factory_.GetWeakPtr()));
+}
+
+void DnsProbeRunner::CallCallback() {
+  DCHECK(!callback_.is_null());
+  DCHECK(!transaction_.get());
+
+  // Clear callback in case it starts a new probe immediately.
+  const base::Closure callback = callback_;
+  callback_.Reset();
+  callback.Run();
+}
+
+}  // namespace chrome_browser_net
diff --git a/chrome/browser/net/dns_probe_runner.h b/chrome/browser/net/dns_probe_runner.h
new file mode 100644
index 0000000..3f294c2
--- /dev/null
+++ b/chrome/browser/net/dns_probe_runner.h
@@ -0,0 +1,85 @@
+// Copyright 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROME_BROWSER_NET_DNS_PROBE_RUNNER_H_
+#define CHROME_BROWSER_NET_DNS_PROBE_RUNNER_H_
+
+#include "base/basictypes.h"
+#include "base/bind.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/memory/weak_ptr.h"
+
+namespace net {
+class DnsClient;
+class DnsResponse;
+class DnsTransaction;
+}
+
+namespace chrome_browser_net {
+
+// Runs DNS probes using a single DnsClient and evaluates the responses.
+// (Currently requests A records for google.com and expects at least one IP
+// address in the response.)
+// Used by DnsProbeService to probe the system and public DNS configurations.
+class DnsProbeRunner {
+ public:
+  static const char* kKnownGoodHostname;
+
+  // Used in histograms; add new entries at the bottom, and don't remove any.
+  enum Result {
+    UNKNOWN,
+    CORRECT,     // Response contains at least one A record.
+    INCORRECT,   // Response claimed success but included no A records.
+    FAILING,     // Response included an error or was malformed.
+    UNREACHABLE  // No response received (timeout, network unreachable, etc.).
+  };
+
+  DnsProbeRunner();
+  ~DnsProbeRunner();
+
+  // Sets the DnsClient that will be used for DNS probes sent by this runner.
+  // Must be called before RunProbe; can be called repeatedly, including during
+  // a probe.  It will not affect an in-flight probe, if one is running.
+  void SetClient(scoped_ptr<net::DnsClient> client);
+
+  // Starts a probe using the client specified with SetClient, which must have
+  // been called before RunProbe.  |callback| will be called asynchronously
+  // when the result is ready, even if it is ready synchronously.  Must not
+  // be called again until the callback is called, but may be called during the
+  // callback.
+  void RunProbe(const base::Closure& callback);
+
+  // Returns true if a probe is running.  Guaranteed to return true after
+  // RunProbe returns, and false during and after the callback.
+  bool IsRunning() const;
+
+  // Returns the result of the last probe.
+  Result result() const { return result_; }
+
+ private:
+  void OnTransactionComplete(net::DnsTransaction* transaction,
+                             int net_error,
+                             const net::DnsResponse* response);
+  void CallCallback();
+
+  base::WeakPtrFactory<DnsProbeRunner> weak_factory_;
+
+  scoped_ptr<net::DnsClient> client_;
+
+  // The callback passed to |RunProbe|.  Cleared right before calling the
+  // callback.
+  base::Closure callback_;
+
+  // The transaction started in |RunProbe| for the DNS probe.  Reset once the
+  // results have been examined.
+  scoped_ptr<net::DnsTransaction> transaction_;
+
+  Result result_;
+
+  DISALLOW_COPY_AND_ASSIGN(DnsProbeRunner);
+};
+
+}  // namespace chrome_browser_net
+
+#endif  // CHROME_BROWSER_NET_DNS_PROBE_RUNNER_H_
diff --git a/chrome/browser/net/dns_probe_runner_unittest.cc b/chrome/browser/net/dns_probe_runner_unittest.cc
new file mode 100644
index 0000000..5519da2
--- /dev/null
+++ b/chrome/browser/net/dns_probe_runner_unittest.cc
@@ -0,0 +1,95 @@
+// Copyright 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/bind.h"
+#include "base/memory/weak_ptr.h"
+#include "base/message_loop.h"
+#include "base/run_loop.h"
+#include "chrome/browser/net/dns_probe_runner.h"
+#include "chrome/browser/net/dns_probe_test_util.h"
+#include "content/public/test/test_browser_thread_bundle.h"
+#include "net/dns/dns_client.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+using base::MessageLoopForIO;
+using base::RunLoop;
+using content::TestBrowserThreadBundle;
+using net::MockDnsClientRule;
+
+namespace chrome_browser_net {
+
+namespace {
+
+class TestDnsProbeRunnerCallback {
+ public:
+  TestDnsProbeRunnerCallback()
+      : callback_(base::Bind(&TestDnsProbeRunnerCallback::OnCalled,
+                             base::Unretained(this))),
+        called_(false) {}
+
+  const base::Closure& callback() const { return callback_; }
+  bool called() const { return called_; }
+
+ private:
+  void OnCalled() {
+    EXPECT_FALSE(called_);
+    called_ = true;
+  }
+
+  base::Closure callback_;
+  bool called_;
+};
+
+class DnsProbeRunnerTest : public testing::Test {
+ protected:
+  void RunTest(MockDnsClientRule::Result query_result,
+               DnsProbeRunner::Result expected_probe_result);
+
+  TestBrowserThreadBundle bundle_;
+  DnsProbeRunner runner_;
+};
+
+void DnsProbeRunnerTest::RunTest(
+    MockDnsClientRule::Result query_result,
+    DnsProbeRunner::Result expected_probe_result) {
+  TestDnsProbeRunnerCallback callback;
+
+  runner_.SetClient(CreateMockDnsClientForProbes(query_result));
+  runner_.RunProbe(callback.callback());
+  EXPECT_TRUE(runner_.IsRunning());
+
+  RunLoop().RunUntilIdle();
+  EXPECT_FALSE(runner_.IsRunning());
+  EXPECT_TRUE(callback.called());
+  EXPECT_EQ(expected_probe_result, runner_.result());
+}
+
+TEST_F(DnsProbeRunnerTest, Probe_OK) {
+  RunTest(MockDnsClientRule::OK, DnsProbeRunner::CORRECT);
+}
+
+TEST_F(DnsProbeRunnerTest, Probe_EMPTY) {
+  RunTest(MockDnsClientRule::EMPTY, DnsProbeRunner::INCORRECT);
+}
+
+TEST_F(DnsProbeRunnerTest, Probe_TIMEOUT) {
+  RunTest(MockDnsClientRule::TIMEOUT, DnsProbeRunner::UNREACHABLE);
+}
+
+TEST_F(DnsProbeRunnerTest, Probe_FAIL_ASYNC) {
+  RunTest(MockDnsClientRule::FAIL_ASYNC, DnsProbeRunner::INCORRECT);
+}
+
+TEST_F(DnsProbeRunnerTest, Probe_FAIL_SYNC) {
+  RunTest(MockDnsClientRule::FAIL_SYNC, DnsProbeRunner::INCORRECT);
+}
+
+TEST_F(DnsProbeRunnerTest, TwoProbes) {
+  RunTest(MockDnsClientRule::OK, DnsProbeRunner::CORRECT);
+  RunTest(MockDnsClientRule::EMPTY, DnsProbeRunner::INCORRECT);
+}
+
+}  // namespace
+
+}  // namespace chrome_browser_net
diff --git a/chrome/browser/net/dns_probe_service.cc b/chrome/browser/net/dns_probe_service.cc
index 156313f..36e28af 100644
--- a/chrome/browser/net/dns_probe_service.cc
+++ b/chrome/browser/net/dns_probe_service.cc
@@ -7,8 +7,6 @@
 #include "base/metrics/field_trial.h"
 #include "base/metrics/histogram.h"
 #include "base/strings/string_number_conversions.h"
-#include "chrome/browser/net/dns_probe_job.h"
-#include "chrome/common/net/net_error_info.h"
 #include "net/base/ip_endpoint.h"
 #include "net/base/net_util.h"
 #include "net/dns/dns_client.h"
@@ -17,7 +15,7 @@
 
 using base::FieldTrialList;
 using base::StringToInt;
-using chrome_common_net::DnsProbeResult;
+using chrome_common_net::DnsProbeStatus;
 using net::DnsClient;
 using net::DnsConfig;
 using net::IPAddressNumber;
@@ -36,8 +34,8 @@ const int kMaxResultAgeMs = 5000;
 
 // The public DNS servers used by the DnsProbeService to verify internet
 // connectivity.
-const char kPublicDnsPrimary[]   = "8.8.8.8";
-const char kPublicDnsSecondary[] = "8.8.4.4";
+const char kGooglePublicDns1[] = "8.8.8.8";
+const char kGooglePublicDns2[] = "8.8.4.4";
 
 IPEndPoint MakeDnsEndPoint(const std::string& dns_ip_literal) {
   IPAddressNumber dns_ip_number;
@@ -46,299 +44,217 @@ IPEndPoint MakeDnsEndPoint(const std::string& dns_ip_literal) {
   return IPEndPoint(dns_ip_number, net::dns_protocol::kDefaultPort);
 }
 
-const int kAttemptsUseDefault = -1;
-
-const char kAttemptsFieldTrialName[] = "DnsProbe-Attempts";
+DnsProbeStatus EvaluateResults(DnsProbeRunner::Result system_result,
+                               DnsProbeRunner::Result public_result) {
+  // If the system DNS is working, assume the domain doesn't exist.
+  if (system_result == DnsProbeRunner::CORRECT)
+    return chrome_common_net::DNS_PROBE_FINISHED_NXDOMAIN;
 
-int GetAttemptsFromFieldTrial() {
-  std::string group = FieldTrialList::FindFullName(kAttemptsFieldTrialName);
-  if (group == "" || group == "default")
-    return kAttemptsUseDefault;
+  // If the system DNS is not working but another public server is, assume the
+  // DNS config is bad (or perhaps the DNS servers are down or broken).
+  if (public_result == DnsProbeRunner::CORRECT)
+    return chrome_common_net::DNS_PROBE_FINISHED_BAD_CONFIG;
 
-  int attempts;
-  if (!StringToInt(group, &attempts))
-   return kAttemptsUseDefault;
+  // If the system DNS is not working and another public server is unreachable,
+  // assume the internet connection is down (note that system DNS may be a
+  // router on the LAN, so it may be reachable but returning errors.)
+  if (public_result == DnsProbeRunner::UNREACHABLE)
+    return chrome_common_net::DNS_PROBE_FINISHED_NO_INTERNET;
 
-  return attempts;
+  // Otherwise: the system DNS is not working and another public server is
+  // responding but with errors or incorrect results.  This is an awkward case;
+  // an invasive captive portal or a restrictive firewall may be intercepting
+  // or rewriting DNS traffic, or the public server may itself be failing or
+  // down.
+  return chrome_common_net::DNS_PROBE_FINISHED_INCONCLUSIVE;
 }
 
-bool IsLocalhost(const IPAddressNumber& ip) {
-  return (ip.size() == net::kIPv4AddressSize)
-         && (ip[0] == 127) && (ip[1] == 0) && (ip[2] == 0) && (ip[3] == 1);
-}
+void HistogramProbe(DnsProbeStatus status, base::TimeDelta elapsed) {
+  DCHECK(chrome_common_net::DnsProbeStatusIsFinished(status));
+
+  int result = status - chrome_common_net::DNS_PROBE_FINISHED_INCONCLUSIVE;
+
+  const int kMaxResult = chrome_common_net::DNS_PROBE_MAX -
+                         chrome_common_net::DNS_PROBE_FINISHED_INCONCLUSIVE;
 
-// The maximum number of nameservers counted in histograms.
-const int kNameserverCountMax = 10;
+  UMA_HISTOGRAM_ENUMERATION("DnsProbe.Status", result, kMaxResult);
+  UMA_HISTOGRAM_MEDIUM_TIMES("DnsProbe.Elapsed", elapsed);
+
+  if (NetworkChangeNotifier::IsOffline()) {
+    UMA_HISTOGRAM_ENUMERATION("DnsProbe.Status_NcnOffline",
+                              result, kMaxResult);
+    UMA_HISTOGRAM_MEDIUM_TIMES("DnsProbe.Elapsed_NcnOffline", elapsed);
+  } else {
+    UMA_HISTOGRAM_ENUMERATION("DnsProbe.Status_NcnOnline",
+                              result, kMaxResult);
+    UMA_HISTOGRAM_MEDIUM_TIMES("DnsProbe.Elapsed_NcnOnline", elapsed);
+  }
+
+  switch (status) {
+    case chrome_common_net::DNS_PROBE_FINISHED_INCONCLUSIVE:
+      UMA_HISTOGRAM_MEDIUM_TIMES("DnsProbe.Elapsed_Unknown",
+                                 elapsed);
+      break;
+    case chrome_common_net::DNS_PROBE_FINISHED_NO_INTERNET:
+      UMA_HISTOGRAM_MEDIUM_TIMES("DnsProbe.Elapsed_NoInternet",
+                                 elapsed);
+      break;
+    case chrome_common_net::DNS_PROBE_FINISHED_BAD_CONFIG:
+      UMA_HISTOGRAM_MEDIUM_TIMES("DnsProbe.Elapsed_BadConfig",
+                                 elapsed);
+      break;
+    case chrome_common_net::DNS_PROBE_FINISHED_NXDOMAIN:
+      UMA_HISTOGRAM_MEDIUM_TIMES("DnsProbe.Elapsed_Nxdomain",
+                                 elapsed);
+      break;
+
+    // These aren't actually results.
+    case chrome_common_net::DNS_PROBE_POSSIBLE:
+    case chrome_common_net::DNS_PROBE_NOT_RUN:
+    case chrome_common_net::DNS_PROBE_STARTED:
+    case chrome_common_net::DNS_PROBE_MAX:
+      NOTREACHED();
+      break;
+  }
+}
 
 }  // namespace
 
 DnsProbeService::DnsProbeService()
-    : system_result_(DnsProbeJob::SERVERS_UNKNOWN),
-      public_result_(DnsProbeJob::SERVERS_UNKNOWN),
-      state_(STATE_NO_RESULTS),
-      result_(chrome_common_net::DNS_PROBE_UNKNOWN),
-      dns_attempts_(GetAttemptsFromFieldTrial()) {
-  NetworkChangeNotifier::AddIPAddressObserver(this);
+    : state_(STATE_NO_RESULT) {
+  NetworkChangeNotifier::AddDNSObserver(this);
+  SetSystemClientToCurrentConfig();
+  SetPublicClientToGooglePublicDns();
 }
 
 DnsProbeService::~DnsProbeService() {
-  NetworkChangeNotifier::RemoveIPAddressObserver(this);
+  NetworkChangeNotifier::RemoveDNSObserver(this);
 }
 
-void DnsProbeService::ProbeDns(const DnsProbeService::CallbackType& callback) {
-  callbacks_.push_back(callback);
+void DnsProbeService::ProbeDns(const DnsProbeService::ProbeCallback& callback) {
+  pending_callbacks_.push_back(callback);
 
-  if (state_ == STATE_RESULTS_CACHED && ResultsExpired())
-    ExpireResults();
+  if (CachedResultIsExpired())
+    ClearCachedResult();
 
   switch (state_) {
-  case STATE_NO_RESULTS:
-    StartProbes();
-    break;
-  case STATE_RESULTS_CACHED:
-    CallCallbacks();
-    break;
-  case STATE_PROBE_RUNNING:
-    // do nothing; probe is already running, and will call the callback
-    break;
+    case STATE_NO_RESULT:
+      StartProbes();
+      break;
+    case STATE_RESULT_CACHED:
+      CallCallbacks();
+      break;
+    case STATE_PROBE_RUNNING:
+      // Do nothing; probe is already running, and will call the callback.
+      break;
   }
 }
 
-scoped_ptr<DnsProbeJob> DnsProbeService::CreateSystemProbeJob(
-    const DnsProbeJob::CallbackType& job_callback) {
-  DnsConfig system_config;
-  GetSystemDnsConfig(&system_config);
-  return CreateProbeJob(system_config, job_callback);
+void DnsProbeService::OnDNSChanged() {
+  ClearCachedResult();
+  SetSystemClientToCurrentConfig();
 }
 
-scoped_ptr<DnsProbeJob> DnsProbeService::CreatePublicProbeJob(
-    const DnsProbeJob::CallbackType& job_callback) {
-  DnsConfig public_config;
-  GetPublicDnsConfig(&public_config);
-  return CreateProbeJob(public_config, job_callback);
+void DnsProbeService::SetSystemClientForTesting(
+    scoped_ptr<DnsClient> system_client) {
+  system_runner_.SetClient(system_client.Pass());
 }
 
-void DnsProbeService::OnIPAddressChanged() {
-  if (state_ == STATE_RESULTS_CACHED)
-    ExpireResults();
+void DnsProbeService::SetPublicClientForTesting(
+    scoped_ptr<DnsClient> public_client) {
+  public_runner_.SetClient(public_client.Pass());
 }
 
-void DnsProbeService::ExpireResults() {
-  DCHECK_EQ(STATE_RESULTS_CACHED, state_);
-
-  state_ = STATE_NO_RESULTS;
-  result_ = chrome_common_net::DNS_PROBE_UNKNOWN;
+void DnsProbeService::ClearCachedResultForTesting() {
+  ClearCachedResult();
 }
 
-void DnsProbeService::StartProbes() {
-  DCHECK_NE(STATE_PROBE_RUNNING, state_);
-  DCHECK(!system_job_.get());
-  DCHECK(!public_job_.get());
-
-  DnsProbeJob::CallbackType job_callback =
-      base::Bind(&DnsProbeService::OnProbeJobComplete,
-                 base::Unretained(this));
-
-  // TODO(ttuttle): Do we want to keep explicit flags for "job done"?
-  //                Or maybe DnsProbeJob should have a "finished" flag?
-  system_result_ = DnsProbeJob::SERVERS_UNKNOWN;
-  public_result_ = DnsProbeJob::SERVERS_UNKNOWN;
-
-  system_job_ = CreateSystemProbeJob(job_callback);
-  public_job_ = CreatePublicProbeJob(job_callback);
-
-  // If we can't create one or both jobs, fail the probe immediately.
-  if (!system_job_.get() || !public_job_.get()) {
-    system_job_.reset();
-    public_job_.reset();
-    state_ = STATE_RESULTS_CACHED;
-    // TODO(ttuttle): Should this be BAD_CONFIG?  Currently I think it only
-    // happens when the system DnsConfig has no servers.
-    result_ = chrome_common_net::DNS_PROBE_UNKNOWN;
-    CallCallbacks();
-    return;
-  }
+void DnsProbeService::SetSystemClientToCurrentConfig() {
+  DnsConfig system_config;
+  NetworkChangeNotifier::GetDnsConfig(&system_config);
+  system_config.search.clear();
+  system_config.attempts = 1;
+  system_config.randomize_ports = false;
 
-  state_ = STATE_PROBE_RUNNING;
-  probe_start_time_ = base::Time::Now();
-}
+  scoped_ptr<DnsClient> system_client(DnsClient::CreateClient(NULL));
+  system_client->SetConfig(system_config);
 
-void DnsProbeService::OnProbesComplete() {
-  DCHECK_EQ(STATE_PROBE_RUNNING, state_);
+  system_runner_.SetClient(system_client.Pass());
+}
 
-  state_ = STATE_RESULTS_CACHED;
-  result_ = EvaluateResults();
+void DnsProbeService::SetPublicClientToGooglePublicDns() {
+  DnsConfig public_config;
+  public_config.nameservers.push_back(MakeDnsEndPoint(kGooglePublicDns1));
+  public_config.nameservers.push_back(MakeDnsEndPoint(kGooglePublicDns2));
+  public_config.attempts = 1;
+  public_config.randomize_ports = false;
 
-  HistogramProbes();
+  scoped_ptr<DnsClient> public_client(DnsClient::CreateClient(NULL));
+  public_client->SetConfig(public_config);
 
-  CallCallbacks();
+  public_runner_.SetClient(public_client.Pass());
 }
 
-void DnsProbeService::HistogramProbes() const {
-  const DnsProbeResult kMaxResult = chrome_common_net::DNS_PROBE_MAX;
-
-  DCHECK_EQ(STATE_RESULTS_CACHED, state_);
-  DCHECK_NE(kMaxResult, result_);
-
-  base::TimeDelta elapsed = base::Time::Now() - probe_start_time_;
+void DnsProbeService::StartProbes() {
+  DCHECK_EQ(STATE_NO_RESULT, state_);
 
-  UMA_HISTOGRAM_ENUMERATION("DnsProbe.Probe.Result", result_, kMaxResult);
-  UMA_HISTOGRAM_MEDIUM_TIMES("DnsProbe.Probe.Elapsed", elapsed);
+  DCHECK(!system_runner_.IsRunning());
+  DCHECK(!public_runner_.IsRunning());
 
-  if (NetworkChangeNotifier::IsOffline()) {
-    UMA_HISTOGRAM_ENUMERATION("DnsProbe.Probe.NcnOffline.Result",
-                              result_, kMaxResult);
-    UMA_HISTOGRAM_MEDIUM_TIMES("DnsProbe.Probe.NcnOffline.Elapsed", elapsed);
-  } else {
-    UMA_HISTOGRAM_ENUMERATION("DnsProbe.Probe.NcnOnline.Result",
-                              result_, kMaxResult);
-    UMA_HISTOGRAM_MEDIUM_TIMES("DnsProbe.Probe.NcnOnline.Elapsed", elapsed);
-  }
+  const base::Closure callback = base::Bind(&DnsProbeService::OnProbeComplete,
+                                            base::Unretained(this));
+  system_runner_.RunProbe(callback);
+  public_runner_.RunProbe(callback);
+  probe_start_time_ = base::Time::Now();
+  state_ = STATE_PROBE_RUNNING;
 
-  switch (result_) {
-  case chrome_common_net::DNS_PROBE_UNKNOWN:
-    UMA_HISTOGRAM_MEDIUM_TIMES("DnsProbe.Probe.ResultUnknown.Elapsed",
-                               elapsed);
-    break;
-  case chrome_common_net::DNS_PROBE_NO_INTERNET:
-    UMA_HISTOGRAM_MEDIUM_TIMES("DnsProbe.Probe.ResultNoInternet.Elapsed",
-                               elapsed);
-    break;
-  case chrome_common_net::DNS_PROBE_BAD_CONFIG:
-    UMA_HISTOGRAM_MEDIUM_TIMES("DnsProbe.Probe.ResultBadConfig.Elapsed",
-                               elapsed);
-
-    // Histogram some extra data to see why BAD_CONFIG is happening.
-    UMA_HISTOGRAM_ENUMERATION(
-        "DnsProbe.Probe.ResultBadConfig.SystemJobResult",
-        system_result_,
-        DnsProbeJob::MAX_RESULT);
-    UMA_HISTOGRAM_CUSTOM_COUNTS(
-        "DnsProbe.Probe.ResultBadConfig.SystemNameserverCount",
-        system_nameserver_count_,
-        0, kNameserverCountMax, kNameserverCountMax + 1);
-    UMA_HISTOGRAM_BOOLEAN(
-        "DnsProbe.Probe.ResultBadConfig.SystemIsLocalhost",
-        system_is_localhost_);
-    break;
-  case chrome_common_net::DNS_PROBE_NXDOMAIN:
-    UMA_HISTOGRAM_MEDIUM_TIMES("DnsProbe.Probe.ResultNxdomain.Elapsed",
-                               elapsed);
-    break;
-  case chrome_common_net::DNS_PROBE_MAX:
-    NOTREACHED();
-    break;
-  }
+  DCHECK(system_runner_.IsRunning());
+  DCHECK(public_runner_.IsRunning());
 }
 
-DnsProbeResult DnsProbeService::EvaluateResults() const {
-  DCHECK_NE(DnsProbeJob::SERVERS_UNKNOWN, system_result_);
-  DCHECK_NE(DnsProbeJob::SERVERS_UNKNOWN, public_result_);
+void DnsProbeService::OnProbeComplete() {
+  DCHECK_EQ(STATE_PROBE_RUNNING, state_);
 
-  // If the system DNS is working, assume the domain doesn't exist.
-  if (system_result_ == DnsProbeJob::SERVERS_CORRECT)
-    return chrome_common_net::DNS_PROBE_NXDOMAIN;
+  if (system_runner_.IsRunning() || public_runner_.IsRunning())
+    return;
 
-  // If the system DNS is not working but another public server is, assume the
-  // DNS config is bad (or perhaps the DNS servers are down or broken).
-  if (public_result_ == DnsProbeJob::SERVERS_CORRECT)
-    return chrome_common_net::DNS_PROBE_BAD_CONFIG;
+  cached_result_ = EvaluateResults(system_runner_.result(),
+                                   public_runner_.result());
+  state_ = STATE_RESULT_CACHED;
 
-  // If the system DNS is not working and another public server is unreachable,
-  // assume the internet connection is down (note that system DNS may be a
-  // router on the LAN, so it may be reachable but returning errors.)
-  if (public_result_ == DnsProbeJob::SERVERS_UNREACHABLE)
-    return chrome_common_net::DNS_PROBE_NO_INTERNET;
+  HistogramProbe(cached_result_, base::Time::Now() - probe_start_time_);
 
-  // Otherwise: the system DNS is not working and another public server is
-  // responding but with errors or incorrect results.  This is an awkward case;
-  // an invasive captive portal or a restrictive firewall may be intercepting
-  // or rewriting DNS traffic, or the public server may itself be failing or
-  // down.
-  return chrome_common_net::DNS_PROBE_UNKNOWN;
+  CallCallbacks();
 }
 
 void DnsProbeService::CallCallbacks() {
-  DCHECK_EQ(STATE_RESULTS_CACHED, state_);
-  DCHECK(!callbacks_.empty());
+  DCHECK_EQ(STATE_RESULT_CACHED, state_);
+  DCHECK(chrome_common_net::DnsProbeStatusIsFinished(cached_result_));
+  DCHECK(!pending_callbacks_.empty());
 
-  std::vector<CallbackType> callbacks = callbacks_;
-  callbacks_.clear();
+  std::vector<ProbeCallback> callbacks;
+  callbacks.swap(pending_callbacks_);
 
-  for (std::vector<CallbackType>::const_iterator i = callbacks.begin();
+  for (std::vector<ProbeCallback>::const_iterator i = callbacks.begin();
        i != callbacks.end(); ++i) {
-    i->Run(result_);
+    i->Run(cached_result_);
   }
 }
 
-scoped_ptr<DnsProbeJob> DnsProbeService::CreateProbeJob(
-    const DnsConfig& dns_config,
-    const DnsProbeJob::CallbackType& job_callback) {
-  if (!dns_config.IsValid())
-    return scoped_ptr<DnsProbeJob>();
-
-  scoped_ptr<DnsClient> dns_client(DnsClient::CreateClient(NULL));
-  dns_client->SetConfig(dns_config);
-  return DnsProbeJob::CreateJob(dns_client.Pass(), job_callback, NULL);
-}
-
-void DnsProbeService::OnProbeJobComplete(DnsProbeJob* job,
-                                         DnsProbeJob::Result result) {
-  DCHECK_EQ(STATE_PROBE_RUNNING, state_);
-
-  if (job == system_job_.get()) {
-    system_result_ = result;
-    system_job_.reset();
-  } else if (job == public_job_.get()) {
-    public_result_ = result;
-    public_job_.reset();
-  } else {
-    NOTREACHED();
-    return;
-  }
-
-  if (system_result_ != DnsProbeJob::SERVERS_UNKNOWN &&
-      public_result_ != DnsProbeJob::SERVERS_UNKNOWN) {
-    OnProbesComplete();
+void DnsProbeService::ClearCachedResult() {
+  if (state_ == STATE_RESULT_CACHED) {
+    state_ = STATE_NO_RESULT;
+    cached_result_ = chrome_common_net::DNS_PROBE_MAX;
   }
 }
 
-void DnsProbeService::GetSystemDnsConfig(DnsConfig* config) {
-  NetworkChangeNotifier::GetDnsConfig(config);
-
-  // DNS probes don't need or want the suffix search list populated
-  config->search.clear();
-
-  if (dns_attempts_ != kAttemptsUseDefault)
-    config->attempts = dns_attempts_;
-
-  // Take notes in case the config turns out to be bad, so we can histogram
-  // some useful data.
-  system_nameserver_count_ = config->nameservers.size();
-  system_is_localhost_ = (system_nameserver_count_ == 1)
-                         && IsLocalhost(config->nameservers[0].address());
-
-  // Disable port randomization.
-  config->randomize_ports = false;
-}
-
-void DnsProbeService::GetPublicDnsConfig(DnsConfig* config) {
-  *config = DnsConfig();
-
-  config->nameservers.push_back(MakeDnsEndPoint(kPublicDnsPrimary));
-  config->nameservers.push_back(MakeDnsEndPoint(kPublicDnsSecondary));
-
-  if (dns_attempts_ != kAttemptsUseDefault)
-    config->attempts = dns_attempts_;
-
-  // Disable port randomization.
-  config->randomize_ports = false;
-}
+bool DnsProbeService::CachedResultIsExpired() const {
+  if (state_ != STATE_RESULT_CACHED)
+    return false;
 
-bool DnsProbeService::ResultsExpired() {
   const base::TimeDelta kMaxResultAge =
       base::TimeDelta::FromMilliseconds(kMaxResultAgeMs);
   return base::Time::Now() - probe_start_time_ > kMaxResultAge;
 }
 
-} // namespace chrome_browser_net
+}  // namespace chrome_browser_net
diff --git a/chrome/browser/net/dns_probe_service.h b/chrome/browser/net/dns_probe_service.h
index a906d75..d1df98e 100644
--- a/chrome/browser/net/dns_probe_service.h
+++ b/chrome/browser/net/dns_probe_service.h
@@ -8,78 +8,70 @@
 #include <vector>
 
 #include "base/basictypes.h"
+#include "base/bind.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/time/time.h"
-#include "chrome/browser/net/dns_probe_job.h"
+#include "chrome/browser/net/dns_probe_runner.h"
 #include "chrome/common/net/net_error_info.h"
 #include "net/base/network_change_notifier.h"
 
 namespace net {
+class DnsClient;
 struct DnsConfig;
 }
 
 namespace chrome_browser_net {
 
-class DnsProbeService : public net::NetworkChangeNotifier::IPAddressObserver {
+// Probes the system and public DNS servers to determine the (probable) cause
+// of a recent DNS-related page load error.  Coalesces multiple probe requests
+// (perhaps from multiple tabs) and caches the results.
+//
+// Uses a single DNS attempt per config, and doesn't randomize source ports.
+class DnsProbeService : public net::NetworkChangeNotifier::DNSObserver {
  public:
-  typedef base::Callback<void(chrome_common_net::DnsProbeResult result)>
-      CallbackType;
+  typedef base::Callback<void(chrome_common_net::DnsProbeStatus result)>
+      ProbeCallback;
 
   DnsProbeService();
   virtual ~DnsProbeService();
 
-  void ProbeDns(const CallbackType& callback);
+  virtual void ProbeDns(const ProbeCallback& callback);
 
-  // NetworkChangeNotifier::IPAddressObserver implementation:
-  virtual void OnIPAddressChanged() OVERRIDE;
+  // NetworkChangeNotifier::DNSObserver implementation:
+  virtual void OnDNSChanged() OVERRIDE;
 
- protected:
-  // This can be called by tests to pretend the cached reuslt has expired.
-  void ExpireResults();
+  void SetSystemClientForTesting(scoped_ptr<net::DnsClient> system_client);
+  void SetPublicClientForTesting(scoped_ptr<net::DnsClient> public_client);
+  void ClearCachedResultForTesting();
 
  private:
   enum State {
-    STATE_NO_RESULTS,
+    STATE_NO_RESULT,
     STATE_PROBE_RUNNING,
-    STATE_RESULTS_CACHED,
+    STATE_RESULT_CACHED,
   };
 
+  void SetSystemClientToCurrentConfig();
+  void SetPublicClientToGooglePublicDns();
+
+  // Starts a probe (runs system and public probes).
   void StartProbes();
-  void OnProbesComplete();
+  void OnProbeComplete();
+  // Calls all |pending_callbacks_| with the |cached_result_|.
   void CallCallbacks();
+  // Clears a cached probe result.
+  void ClearCachedResult();
+
+  bool CachedResultIsExpired() const;
 
-  void OnProbeJobComplete(DnsProbeJob* job, DnsProbeJob::Result result);
-  chrome_common_net::DnsProbeResult EvaluateResults() const;
-  void HistogramProbes() const;
-
-  // These are expected to be overridden by tests to return mock jobs.
-  virtual scoped_ptr<DnsProbeJob> CreateSystemProbeJob(
-      const DnsProbeJob::CallbackType& job_callback);
-  virtual scoped_ptr<DnsProbeJob> CreatePublicProbeJob(
-      const DnsProbeJob::CallbackType& job_callback);
-
-  scoped_ptr<DnsProbeJob> CreateProbeJob(
-      const net::DnsConfig& dns_config,
-      const DnsProbeJob::CallbackType& job_callback);
-  void GetSystemDnsConfig(net::DnsConfig* config);
-  void GetPublicDnsConfig(net::DnsConfig* config);
-  bool ResultsExpired();
-
-  scoped_ptr<DnsProbeJob> system_job_;
-  scoped_ptr<DnsProbeJob> public_job_;
-  DnsProbeJob::Result system_result_;
-  DnsProbeJob::Result public_result_;
-  std::vector<CallbackType> callbacks_;
   State state_;
-  chrome_common_net::DnsProbeResult result_;
+  std::vector<ProbeCallback> pending_callbacks_;
   base::Time probe_start_time_;
-  // How many DNS request attempts the probe jobs will make before giving up
-  // (Overrides the attempts field in the system DnsConfig.)
-  const int dns_attempts_;
-  // How many nameservers the system config has.
-  int system_nameserver_count_;
-  // Whether the only system nameserver is 127.0.0.1.
-  bool system_is_localhost_;
+  chrome_common_net::DnsProbeStatus cached_result_;
+
+  // DnsProbeRunners for the system DNS configuration and a public DNS server.
+  DnsProbeRunner system_runner_;
+  DnsProbeRunner public_runner_;
 
   DISALLOW_COPY_AND_ASSIGN(DnsProbeService);
 };
diff --git a/chrome/browser/net/dns_probe_service_unittest.cc b/chrome/browser/net/dns_probe_service_unittest.cc
index 15cbb44..d8b55eb 100644
--- a/chrome/browser/net/dns_probe_service_unittest.cc
+++ b/chrome/browser/net/dns_probe_service_unittest.cc
@@ -9,111 +9,28 @@
 #include "base/memory/weak_ptr.h"
 #include "base/message_loop.h"
 #include "base/run_loop.h"
-#include "chrome/browser/net/dns_probe_job.h"
+#include "chrome/browser/net/dns_probe_runner.h"
+#include "chrome/browser/net/dns_probe_test_util.h"
 #include "chrome/common/net/net_error_info.h"
+#include "content/public/test/test_browser_thread_bundle.h"
+#include "net/dns/dns_test_util.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
-using chrome_common_net::DnsProbeResult;
+using base::MessageLoopForIO;
+using base::RunLoop;
+using chrome_common_net::DnsProbeStatus;
+using content::TestBrowserThreadBundle;
+using net::MockDnsClientRule;
 
 namespace chrome_browser_net {
 
 namespace {
 
-class MockDnsProbeJob : public DnsProbeJob {
- public:
-  MockDnsProbeJob(const CallbackType& callback,
-                  DnsProbeJob::Result result)
-      : weak_factory_(this) {
-    base::MessageLoop::current()->PostTask(
-        FROM_HERE,
-        base::Bind(&MockDnsProbeJob::CallCallback,
-                   weak_factory_.GetWeakPtr(),
-                   callback,
-                   result));
-  }
-
-  virtual ~MockDnsProbeJob() { }
-
- private:
-  void CallCallback(const CallbackType& callback, Result result) {
-    callback.Run(this, result);
-  }
-
-  base::WeakPtrFactory<MockDnsProbeJob> weak_factory_;
-};
-
-class TestDnsProbeService : public DnsProbeService {
- public:
-  TestDnsProbeService()
-      : DnsProbeService(),
-        system_job_created_(false),
-        public_job_created_(false),
-        mock_system_result_(DnsProbeJob::SERVERS_UNKNOWN),
-        mock_public_result_(DnsProbeJob::SERVERS_UNKNOWN),
-        mock_system_fail_(false) {
-  }
-
-  virtual ~TestDnsProbeService() { }
-
-  void set_mock_results(
-      DnsProbeJob::Result mock_system_result,
-      DnsProbeJob::Result mock_public_result) {
-    mock_system_result_ = mock_system_result;
-    mock_public_result_ = mock_public_result;
-  }
-
-  void set_mock_system_fail(bool mock_system_fail) {
-    mock_system_fail_ = mock_system_fail;
-  }
-
-  bool jobs_created(void) {
-    return system_job_created_ && public_job_created_;
-  }
-
-  void ResetJobsCreated() {
-    system_job_created_ = false;
-    public_job_created_ = false;
-  }
-
-  void MockExpireResults() {
-    ExpireResults();
-  }
-
-  bool system_job_created_;
-  bool public_job_created_;
-
- private:
-  // Override methods in DnsProbeService to return mock jobs:
-
-  virtual scoped_ptr<DnsProbeJob> CreateSystemProbeJob(
-      const DnsProbeJob::CallbackType& job_callback) OVERRIDE {
-    if (mock_system_fail_)
-      return scoped_ptr<DnsProbeJob>();
-
-    system_job_created_ = true;
-    return scoped_ptr<DnsProbeJob>(
-        new MockDnsProbeJob(job_callback,
-                            mock_system_result_));
-  }
-
-  virtual scoped_ptr<DnsProbeJob> CreatePublicProbeJob(
-      const DnsProbeJob::CallbackType& job_callback) OVERRIDE {
-    public_job_created_ = true;
-    return scoped_ptr<DnsProbeJob>(
-        new MockDnsProbeJob(job_callback,
-                            mock_public_result_));
-  }
-
-  DnsProbeJob::Result mock_system_result_;
-  DnsProbeJob::Result mock_public_result_;
-  bool mock_system_fail_;
-};
-
 class DnsProbeServiceTest : public testing::Test {
  public:
   DnsProbeServiceTest()
       : callback_called_(false),
-        callback_result_(chrome_common_net::DNS_PROBE_UNKNOWN) {
+        callback_result_(chrome_common_net::DNS_PROBE_MAX) {
   }
 
   void Probe() {
@@ -121,98 +38,94 @@ class DnsProbeServiceTest : public testing::Test {
                                  base::Unretained(this)));
   }
 
-  void RunUntilIdle() {
-    base::RunLoop run_loop;
-    run_loop.RunUntilIdle();
-  }
-
   void Reset() {
-    service_.ResetJobsCreated();
     callback_called_ = false;
   }
 
-  base::MessageLoopForIO message_loop_;
-  TestDnsProbeService service_;
-  bool callback_called_;
-  DnsProbeResult callback_result_;
+ protected:
+  void SetRules(MockDnsClientRule::Result system_query_result,
+                MockDnsClientRule::Result public_query_result) {
+    service_.SetSystemClientForTesting(
+        CreateMockDnsClientForProbes(system_query_result));
+    service_.SetPublicClientForTesting(
+        CreateMockDnsClientForProbes(public_query_result));
+  }
+
+  void RunTest(MockDnsClientRule::Result system_query_result,
+               MockDnsClientRule::Result public_query_result,
+               DnsProbeStatus expected_result) {
+    Reset();
+    SetRules(system_query_result, public_query_result);
+
+    Probe();
+    RunLoop().RunUntilIdle();
+    EXPECT_TRUE(callback_called_);
+    EXPECT_EQ(expected_result, callback_result_);
+  }
+
+  void ClearCachedResult() {
+    service_.ClearCachedResultForTesting();
+  }
 
  private:
-  void ProbeCallback(DnsProbeResult result) {
+  void ProbeCallback(DnsProbeStatus result) {
+    EXPECT_FALSE(callback_called_);
     callback_called_ = true;
     callback_result_ = result;
   }
+
+  DnsProbeService service_;
+  bool callback_called_;
+  DnsProbeStatus callback_result_;
+  TestBrowserThreadBundle bundle_;
 };
 
-TEST_F(DnsProbeServiceTest, Null) {
+TEST_F(DnsProbeServiceTest, Probe_OK_OK) {
+  RunTest(MockDnsClientRule::OK, MockDnsClientRule::OK,
+          chrome_common_net::DNS_PROBE_FINISHED_NXDOMAIN);
 }
 
-TEST_F(DnsProbeServiceTest, Probe) {
-  service_.set_mock_results(DnsProbeJob::SERVERS_CORRECT,
-                            DnsProbeJob::SERVERS_CORRECT);
-
-  Probe();
-  EXPECT_TRUE(service_.jobs_created());
-  EXPECT_FALSE(callback_called_);
-
-  RunUntilIdle();
-  EXPECT_TRUE(callback_called_);
-  EXPECT_EQ(chrome_common_net::DNS_PROBE_NXDOMAIN, callback_result_);
+TEST_F(DnsProbeServiceTest, Probe_TIMEOUT_OK) {
+  RunTest(MockDnsClientRule::TIMEOUT, MockDnsClientRule::OK,
+          chrome_common_net::DNS_PROBE_FINISHED_BAD_CONFIG);
 }
 
-TEST_F(DnsProbeServiceTest, Cache) {
-  service_.set_mock_results(DnsProbeJob::SERVERS_CORRECT,
-                            DnsProbeJob::SERVERS_CORRECT);
-
-  Probe();
-  RunUntilIdle();
-  Reset();
-
-  // Cached NXDOMAIN result should persist.
-
-  Probe();
-  EXPECT_FALSE(service_.jobs_created());
-
-  RunUntilIdle();
-  EXPECT_TRUE(callback_called_);
-  EXPECT_EQ(chrome_common_net::DNS_PROBE_NXDOMAIN, callback_result_);
+TEST_F(DnsProbeServiceTest, Probe_TIMEOUT_TIMEOUT) {
+  RunTest(MockDnsClientRule::TIMEOUT, MockDnsClientRule::TIMEOUT,
+          chrome_common_net::DNS_PROBE_FINISHED_NO_INTERNET);
 }
 
-TEST_F(DnsProbeServiceTest, Expired) {
-  service_.set_mock_results(DnsProbeJob::SERVERS_CORRECT,
-                            DnsProbeJob::SERVERS_CORRECT);
-
-  Probe();
-  EXPECT_TRUE(service_.jobs_created());
-
-  RunUntilIdle();
-  EXPECT_TRUE(callback_called_);
-  EXPECT_EQ(chrome_common_net::DNS_PROBE_NXDOMAIN, callback_result_);
-
-  Reset();
-
-  service_.MockExpireResults();
-
-  Probe();
-  EXPECT_TRUE(service_.jobs_created());
-
-  RunUntilIdle();
-  EXPECT_TRUE(callback_called_);
-  EXPECT_EQ(chrome_common_net::DNS_PROBE_NXDOMAIN, callback_result_);
+TEST_F(DnsProbeServiceTest, Probe_OK_FAIL_SYNC) {
+  RunTest(MockDnsClientRule::OK, MockDnsClientRule::FAIL_SYNC,
+          chrome_common_net::DNS_PROBE_FINISHED_NXDOMAIN);
 }
 
-TEST_F(DnsProbeServiceTest, SystemFail) {
-  service_.set_mock_results(DnsProbeJob::SERVERS_CORRECT,
-                            DnsProbeJob::SERVERS_CORRECT);
-  service_.set_mock_system_fail(true);
+TEST_F(DnsProbeServiceTest, Probe_FAIL_SYNC_OK) {
+  RunTest(MockDnsClientRule::FAIL_SYNC, MockDnsClientRule::OK,
+          chrome_common_net::DNS_PROBE_FINISHED_BAD_CONFIG);
+}
 
-  Probe();
-  EXPECT_TRUE(callback_called_);
-  EXPECT_EQ(chrome_common_net::DNS_PROBE_UNKNOWN, callback_result_);
+TEST_F(DnsProbeServiceTest, Probe_FAIL_SYNC_FAIL_SYNC) {
+  RunTest(MockDnsClientRule::FAIL_SYNC, MockDnsClientRule::FAIL_SYNC,
+          chrome_common_net::DNS_PROBE_FINISHED_INCONCLUSIVE);
+}
 
-  Reset();
+TEST_F(DnsProbeServiceTest, Cache) {
+  RunTest(MockDnsClientRule::OK, MockDnsClientRule::OK,
+          chrome_common_net::DNS_PROBE_FINISHED_NXDOMAIN);
+  // Cached NXDOMAIN result should persist, not the result from the new rules.
+  RunTest(MockDnsClientRule::TIMEOUT, MockDnsClientRule::TIMEOUT,
+          chrome_common_net::DNS_PROBE_FINISHED_NXDOMAIN);
+}
 
-  RunUntilIdle();
-  EXPECT_FALSE(callback_called_);
+TEST_F(DnsProbeServiceTest, Expire) {
+  RunTest(MockDnsClientRule::OK, MockDnsClientRule::OK,
+          chrome_common_net::DNS_PROBE_FINISHED_NXDOMAIN);
+  // Pretend cache expires.
+  ClearCachedResult();
+  // New rules should apply, since a new probe should be run.
+  RunTest(MockDnsClientRule::TIMEOUT, MockDnsClientRule::TIMEOUT,
+          chrome_common_net::DNS_PROBE_FINISHED_NO_INTERNET);
 }
 
 }  // namespace
diff --git a/chrome/browser/net/dns_probe_test_util.cc b/chrome/browser/net/dns_probe_test_util.cc
new file mode 100644
index 0000000..88d481d
--- /dev/null
+++ b/chrome/browser/net/dns_probe_test_util.cc
@@ -0,0 +1,37 @@
+// Copyright 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "chrome/browser/net/dns_probe_test_util.h"
+
+#include "chrome/browser/net/dns_probe_runner.h"
+#include "net/dns/dns_config_service.h"
+#include "net/dns/dns_protocol.h"
+
+using net::DnsClient;
+using net::DnsConfig;
+using net::IPAddressNumber;
+using net::IPEndPoint;
+using net::MockDnsClientRule;
+using net::MockDnsClientRuleList;
+using net::ParseIPLiteralToNumber;
+
+namespace chrome_browser_net {
+
+scoped_ptr<DnsClient> CreateMockDnsClientForProbes(
+    MockDnsClientRule::Result result) {
+  DnsConfig config;
+  IPAddressNumber dns_ip;
+  ParseIPLiteralToNumber("192.168.1.1", &dns_ip);
+  const uint16 kDnsPort = net::dns_protocol::kDefaultPort;
+  config.nameservers.push_back(IPEndPoint(dns_ip, kDnsPort));
+
+  const uint16 kTypeA = net::dns_protocol::kTypeA;
+  MockDnsClientRuleList rules;
+  rules.push_back(
+      MockDnsClientRule(DnsProbeRunner::kKnownGoodHostname, kTypeA, result));
+
+  return CreateMockDnsClient(config, rules).Pass();
+}
+
+}  // namespace chrome_browser_net
diff --git a/chrome/browser/net/dns_probe_test_util.h b/chrome/browser/net/dns_probe_test_util.h
new file mode 100644
index 0000000..0f36174
--- /dev/null
+++ b/chrome/browser/net/dns_probe_test_util.h
@@ -0,0 +1,21 @@
+// Copyright 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CHROME_BROWSER_NET_DNS_PROBE_TEST_UTIL_H_
+#define CHROME_BROWSER_NET_DNS_PROBE_TEST_UTIL_H_
+
+#include "base/memory/scoped_ptr.h"
+#include "net/dns/dns_client.h"
+#include "net/dns/dns_test_util.h"
+
+namespace chrome_browser_net {
+
+// Creates a mock DNS client with a single rule for the known-good query
+// (currently google.com) that returns |result|.
+scoped_ptr<net::DnsClient> CreateMockDnsClientForProbes(
+    net::MockDnsClientRule::Result result);
+
+}  // namespace chrome_browser_net
+
+#endif  // CHROME_BROWSER_NET_DNS_PROBE_TEST_UTIL_H_
diff --git a/chrome/browser/net/net_error_tab_helper.cc b/chrome/browser/net/net_error_tab_helper.cc
index c7189a9..6f20a8a 100644
--- a/chrome/browser/net/net_error_tab_helper.cc
+++ b/chrome/browser/net/net_error_tab_helper.cc
@@ -18,7 +18,8 @@
 #include "net/base/net_errors.h"
 
 using base::FieldTrialList;
-using chrome_common_net::DnsProbeResult;
+using chrome_common_net::DnsProbeStatus;
+using chrome_common_net::DnsProbeStatusToString;
 using content::BrowserContext;
 using content::BrowserThread;
 using content::PageTransition;
@@ -32,9 +33,6 @@ namespace chrome_browser_net {
 
 namespace {
 
-const char kDnsProbeFieldTrialName[] = "DnsProbe-Enable";
-const char kDnsProbeFieldTrialEnableGroupName[] = "enable";
-
 static NetErrorTabHelper::TestingState testing_state_ =
     NetErrorTabHelper::TESTING_DEFAULT;
 
@@ -45,48 +43,24 @@ bool IsDnsError(int net_error) {
          net_error == net::ERR_NAME_RESOLUTION_FAILED;
 }
 
-bool GetEnabledByTrial() {
-  return (FieldTrialList::FindFullName(kDnsProbeFieldTrialName)
-          == kDnsProbeFieldTrialEnableGroupName);
-}
-
-NetErrorTracker::FrameType GetFrameType(bool is_main_frame) {
-  return is_main_frame ? NetErrorTracker::FRAME_MAIN
-                       : NetErrorTracker::FRAME_SUB;
-}
-
-NetErrorTracker::PageType GetPageType(bool is_error_page) {
-  return is_error_page ? NetErrorTracker::PAGE_ERROR
-                       : NetErrorTracker::PAGE_NORMAL;
-}
-
-NetErrorTracker::ErrorType GetErrorType(int net_error) {
-  return IsDnsError(net_error) ? NetErrorTracker::ERROR_DNS
-                               : NetErrorTracker::ERROR_OTHER;
-}
-
 void OnDnsProbeFinishedOnIOThread(
-    const base::Callback<void(DnsProbeResult)>& callback,
-    DnsProbeResult result) {
+    const base::Callback<void(DnsProbeStatus)>& callback,
+    DnsProbeStatus result) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
 
-  DVLOG(1) << "DNS probe finished with result " << result;
-
   BrowserThread::PostTask(
       BrowserThread::UI,
       FROM_HERE,
       base::Bind(callback, result));
 }
 
-// We can only access g_browser_process->io_thread() from the browser thread,
-// so we have to pass it in to the callback instead of dereferencing it here.
+// Can only access g_browser_process->io_thread() from the browser thread,
+// so have to pass it in to the callback instead of dereferencing it here.
 void StartDnsProbeOnIOThread(
-    const base::Callback<void(DnsProbeResult)>& callback,
+    const base::Callback<void(DnsProbeStatus)>& callback,
     IOThread* io_thread) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::IO));
 
-  DVLOG(1) << "Starting DNS probe";
-
   DnsProbeService* probe_service =
       io_thread->globals()->dns_probe_service.get();
 
@@ -113,8 +87,10 @@ void NetErrorTabHelper::DidStartProvisionalLoadForFrame(
     RenderViewHost* render_view_host) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 
-  tracker_.OnStartProvisionalLoad(GetFrameType(is_main_frame),
-                                  GetPageType(is_error_page));
+  if (!is_main_frame)
+    return;
+
+  is_error_page_ = is_error_page;
 }
 
 void NetErrorTabHelper::DidCommitProvisionalLoadForFrame(
@@ -125,7 +101,21 @@ void NetErrorTabHelper::DidCommitProvisionalLoadForFrame(
     RenderViewHost* render_view_host) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 
-  tracker_.OnCommitProvisionalLoad(GetFrameType(is_main_frame));
+  if (!is_main_frame)
+    return;
+
+  // Resend status every time an error page commits; this is somewhat spammy,
+  // but ensures that the status will make it to the real error page, even if
+  // the link doctor loads a blank intermediate page or the tab switches
+  // renderer processes.
+  if (is_error_page_ && dns_error_active_) {
+    dns_error_page_committed_ = true;
+    DVLOG(1) << "Committed error page; resending status.";
+    SendInfo();
+  } else {
+    dns_error_active_ = false;
+    dns_error_page_committed_ = false;
+  }
 }
 
 void NetErrorTabHelper::DidFailProvisionalLoad(
@@ -137,75 +127,70 @@ void NetErrorTabHelper::DidFailProvisionalLoad(
     RenderViewHost* render_view_host) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 
-  tracker_.OnFailProvisionalLoad(GetFrameType(is_main_frame),
-                                 GetErrorType(error_code));
-}
+  if (!is_main_frame)
+    return;
 
-void NetErrorTabHelper::DidFinishLoad(
-    int64 frame_id,
-    const GURL& validated_url,
-    bool is_main_frame,
-    RenderViewHost* render_view_host) {
-  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
-
-  tracker_.OnFinishLoad(GetFrameType(is_main_frame));
+  if (IsDnsError(error_code)) {
+    dns_error_active_ = true;
+    OnMainFrameDnsError();
+  }
 }
 
 NetErrorTabHelper::NetErrorTabHelper(WebContents* contents)
     : WebContentsObserver(contents),
       weak_factory_(this),
-      tracker_(base::Bind(&NetErrorTabHelper::TrackerCallback,
-                          weak_factory_.GetWeakPtr())),
-      dns_error_page_state_(NetErrorTracker::DNS_ERROR_PAGE_NONE),
-      dns_probe_state_(DNS_PROBE_NONE),
-      enabled_by_trial_(GetEnabledByTrial()) {
+      is_error_page_(false),
+      dns_error_active_(false),
+      dns_error_page_committed_(false),
+      dns_probe_status_(chrome_common_net::DNS_PROBE_POSSIBLE),
+      enabled_by_trial_(chrome_common_net::DnsProbesEnabledByFieldTrial()) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 
-  InitializePref(contents);
+  // If this helper is under test, it won't have a WebContents.
+  if (contents)
+    InitializePref(contents);
 }
 
-void NetErrorTabHelper::TrackerCallback(
-    NetErrorTracker::DnsErrorPageState state) {
-  dns_error_page_state_ = state;
-
-  MaybePostStartDnsProbeTask();
-  MaybeSendInfo();
+void NetErrorTabHelper::OnMainFrameDnsError() {
+  if (ProbesAllowed()) {
+    // Don't start more than one probe at a time.
+    if (dns_probe_status_ != chrome_common_net::DNS_PROBE_STARTED) {
+      StartDnsProbe();
+      dns_probe_status_ = chrome_common_net::DNS_PROBE_STARTED;
+    }
+  } else {
+    dns_probe_status_ = chrome_common_net::DNS_PROBE_NOT_RUN;
+  }
 }
 
-void NetErrorTabHelper::MaybePostStartDnsProbeTask() {
+void NetErrorTabHelper::StartDnsProbe() {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  DCHECK(dns_error_active_);
+  DCHECK_NE(chrome_common_net::DNS_PROBE_STARTED, dns_probe_status_);
 
-  if (dns_error_page_state_ != NetErrorTracker::DNS_ERROR_PAGE_NONE &&
-      dns_probe_state_ != DNS_PROBE_STARTED &&
-      ProbesAllowed()) {
-    BrowserThread::PostTask(
-        BrowserThread::IO,
-        FROM_HERE,
-        base::Bind(&StartDnsProbeOnIOThread,
-                   base::Bind(&NetErrorTabHelper::OnDnsProbeFinished,
-                              weak_factory_.GetWeakPtr()),
-                   g_browser_process->io_thread()));
-    dns_probe_state_ = DNS_PROBE_STARTED;
-  }
+  DVLOG(1) << "Starting DNS probe.";
+
+  BrowserThread::PostTask(
+      BrowserThread::IO,
+      FROM_HERE,
+      base::Bind(&StartDnsProbeOnIOThread,
+                 base::Bind(&NetErrorTabHelper::OnDnsProbeFinished,
+                            weak_factory_.GetWeakPtr()),
+                 g_browser_process->io_thread()));
 }
 
-void NetErrorTabHelper::OnDnsProbeFinished(DnsProbeResult result) {
+void NetErrorTabHelper::OnDnsProbeFinished(DnsProbeStatus result) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
-  DCHECK_EQ(DNS_PROBE_STARTED, dns_probe_state_);
+  DCHECK_EQ(chrome_common_net::DNS_PROBE_STARTED, dns_probe_status_);
+  DCHECK(chrome_common_net::DnsProbeStatusIsFinished(result));
 
-  dns_probe_result_ = result;
-  dns_probe_state_ = DNS_PROBE_FINISHED;
+  DVLOG(1) << "Finished DNS probe with result "
+           << DnsProbeStatusToString(result) << ".";
 
-  MaybeSendInfo();
-}
+  dns_probe_status_ = result;
 
-void NetErrorTabHelper::MaybeSendInfo() {
-  if (dns_error_page_state_ == NetErrorTracker::DNS_ERROR_PAGE_LOADED &&
-      dns_probe_state_ == DNS_PROBE_FINISHED) {
-    DVLOG(1) << "Sending result " << dns_probe_result_ << " to renderer";
-    Send(new ChromeViewMsg_NetErrorInfo(routing_id(), dns_probe_result_));
-    dns_probe_state_ = DNS_PROBE_NONE;
-  }
+  if (dns_error_page_committed_)
+    SendInfo();
 }
 
 void NetErrorTabHelper::InitializePref(WebContents* contents) {
@@ -226,4 +211,15 @@ bool NetErrorTabHelper::ProbesAllowed() const {
   return enabled_by_trial_ && *resolve_errors_with_web_service_;
 }
 
+void NetErrorTabHelper::SendInfo() {
+  DCHECK_NE(chrome_common_net::DNS_PROBE_POSSIBLE, dns_probe_status_);
+  DCHECK(dns_error_page_committed_);
+
+  DVLOG(1) << "Sending status " << DnsProbeStatusToString(dns_probe_status_);
+  Send(new ChromeViewMsg_NetErrorInfo(routing_id(), dns_probe_status_));
+
+  if (!dns_probe_status_snoop_callback_.is_null())
+    dns_probe_status_snoop_callback_.Run(dns_probe_status_);
+}
+
 }  // namespace chrome_browser_net
diff --git a/chrome/browser/net/net_error_tab_helper.h b/chrome/browser/net/net_error_tab_helper.h
index e48fa9f..fd0553e 100644
--- a/chrome/browser/net/net_error_tab_helper.h
+++ b/chrome/browser/net/net_error_tab_helper.h
@@ -6,12 +6,12 @@
 #define CHROME_BROWSER_NET_NET_ERROR_TAB_HELPER_H_
 
 #include "base/basictypes.h"
+#include "base/bind.h"
 #include "base/compiler_specific.h"
 #include "base/memory/weak_ptr.h"
 #include "base/prefs/pref_member.h"
 #include "chrome/browser/net/dns_probe_service.h"
 #include "chrome/common/net/net_error_info.h"
-#include "chrome/common/net/net_error_tracker.h"
 #include "content/public/browser/web_contents_observer.h"
 #include "content/public/browser/web_contents_user_data.h"
 
@@ -30,10 +30,21 @@ class NetErrorTabHelper
     TESTING_FORCE_ENABLED
   };
 
+  typedef base::Callback<void(chrome_common_net::DnsProbeStatus)>
+      DnsProbeStatusSnoopCallback;
+
   virtual ~NetErrorTabHelper();
 
   static void set_state_for_testing(TestingState testing_state);
 
+  // Sets a callback that will be called immediately after the helper sends
+  // a NetErrorHelper IPC.  (Used by the DNS probe browser test to know when to
+  // check the error page for updates, instead of polling.)
+  void set_dns_probe_status_snoop_callback_for_testing(
+      const DnsProbeStatusSnoopCallback& dns_probe_status_snoop_callback) {
+    dns_probe_status_snoop_callback_ = dns_probe_status_snoop_callback;
+  }
+
   // content::WebContentsObserver implementation.
   virtual void DidStartProvisionalLoadForFrame(
       int64 frame_id,
@@ -59,43 +70,50 @@ class NetErrorTabHelper
       const string16& error_description,
       content::RenderViewHost* render_view_host) OVERRIDE;
 
-  virtual void DidFinishLoad(
-      int64 frame_id,
-      const GURL& validated_url,
-      bool is_main_frame,
-      content::RenderViewHost* render_view_host) OVERRIDE;
-
- private:
-  friend class content::WebContentsUserData<NetErrorTabHelper>;
-
-  enum DnsProbeState {
-    DNS_PROBE_NONE,
-    DNS_PROBE_STARTED,
-    DNS_PROBE_FINISHED
-  };
-
+ protected:
   // |contents| is the WebContents of the tab this NetErrorTabHelper is
   // attached to.
   explicit NetErrorTabHelper(content::WebContents* contents);
+  virtual void StartDnsProbe();
+  virtual void SendInfo();
+  void OnDnsProbeFinished(chrome_common_net::DnsProbeStatus result);
+
+  chrome_common_net::DnsProbeStatus dns_probe_status() const {
+    return dns_probe_status_;
+  }
+
+ private:
+  friend class content::WebContentsUserData<NetErrorTabHelper>;
 
-  void TrackerCallback(NetErrorTracker::DnsErrorPageState state);
-  void MaybePostStartDnsProbeTask();
-  void OnDnsProbeFinished(chrome_common_net::DnsProbeResult result);
-  void MaybeSendInfo();
+  void OnMainFrameDnsError();
 
   void InitializePref(content::WebContents* contents);
   bool ProbesAllowed() const;
 
   base::WeakPtrFactory<NetErrorTabHelper> weak_factory_;
 
-  NetErrorTracker tracker_;
-  NetErrorTracker::DnsErrorPageState dns_error_page_state_;
+  // True if the last provisional load that started was for an error page.
+  bool is_error_page_;
+
+  // True if the helper has seen a main frame page load fail with a DNS error,
+  // but has not yet seen a new page commit successfully afterwards.
+  bool dns_error_active_;
+
+  // True if the helper has seen an error page commit while |dns_error_active_|
+  // is true.  (This should never be true if |dns_error_active_| is false.)
+  bool dns_error_page_committed_;
 
-  DnsProbeState dns_probe_state_;
-  chrome_common_net::DnsProbeResult dns_probe_result_;
+  // The status of a DNS probe that may or may not have started or finished.
+  // Since the renderer can change out from under the helper (in cross-process
+  // navigations), it re-sends the status whenever an error page commits.
+  chrome_common_net::DnsProbeStatus dns_probe_status_;
 
   // Whether we are enabled to run by the DnsProbe-Enable field trial.
   const bool enabled_by_trial_;
+
+  // Optional callback for browser test to snoop on outgoing NetErrorInfo IPCs.
+  DnsProbeStatusSnoopCallback dns_probe_status_snoop_callback_;
+
   // "Use a web service to resolve navigation errors" preference is required
   // to allow probes.
   BooleanPrefMember resolve_errors_with_web_service_;
diff --git a/chrome/browser/net/net_error_tab_helper_unittest.cc b/chrome/browser/net/net_error_tab_helper_unittest.cc
new file mode 100644
index 0000000..3a029bb
--- /dev/null
+++ b/chrome/browser/net/net_error_tab_helper_unittest.cc
@@ -0,0 +1,392 @@
+// Copyright 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "chrome/browser/net/net_error_tab_helper.h"
+
+#include "base/message_loop.h"
+#include "chrome/common/net/net_error_info.h"
+#include "content/public/browser/browser_thread.h"
+#include "content/public/common/page_transition_types.h"
+#include "content/public/test/test_browser_thread.h"
+#include "net/base/net_errors.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+using base::MessageLoop;
+using chrome_browser_net::NetErrorTabHelper;
+using chrome_common_net::DnsProbeStatus;
+using content::BrowserThread;
+using content::TestBrowserThread;
+
+class TestNetErrorTabHelper : public NetErrorTabHelper {
+ public:
+  TestNetErrorTabHelper()
+      : NetErrorTabHelper(NULL),
+        mock_probe_running_(false),
+        last_status_sent_(chrome_common_net::DNS_PROBE_MAX),
+        mock_sent_count_(0) {}
+
+  void FinishProbe(DnsProbeStatus status) {
+    EXPECT_TRUE(mock_probe_running_);
+    OnDnsProbeFinished(status);
+    mock_probe_running_ = false;
+  }
+
+  bool mock_probe_running() const { return mock_probe_running_; }
+  DnsProbeStatus last_status_sent() const { return last_status_sent_; }
+  int mock_sent_count() const { return mock_sent_count_; }
+
+ private:
+  virtual void StartDnsProbe() OVERRIDE {
+    EXPECT_FALSE(mock_probe_running_);
+    mock_probe_running_ = true;
+  }
+
+  virtual void SendInfo() OVERRIDE {
+    last_status_sent_ = dns_probe_status();
+    mock_sent_count_++;
+  }
+
+  bool mock_probe_running_;
+  DnsProbeStatus last_status_sent_;
+  int mock_sent_count_;
+};
+
+class NetErrorTabHelperTest : public testing::Test {
+ protected:
+  enum MainFrame { SUB_FRAME, MAIN_FRAME };
+  enum ErrorPage { NORMAL_PAGE, ERROR_PAGE };
+  enum ErrorType { DNS_ERROR, OTHER_ERROR };
+
+  NetErrorTabHelperTest()
+      : fake_ui_thread_(BrowserThread::UI, &message_loop_) {
+    NetErrorTabHelper::set_state_for_testing(
+        NetErrorTabHelper::TESTING_FORCE_ENABLED);
+  }
+
+  void StartProvisionalLoad(MainFrame main_frame, ErrorPage error_page) {
+    tab_helper_.DidStartProvisionalLoadForFrame(
+        1,  // frame_id
+        0,  // parent_frame_id
+        (main_frame == MAIN_FRAME),
+        bogus_url_,  // validated_url
+        (error_page == ERROR_PAGE),
+        false,  // is_iframe_srcdoc
+        NULL);  // render_view_host
+  }
+
+  void CommitProvisionalLoad(MainFrame main_frame) {
+    tab_helper_.DidCommitProvisionalLoadForFrame(
+        1,  // frame id
+        (main_frame == MAIN_FRAME),
+        bogus_url_,  // url
+        content::PAGE_TRANSITION_TYPED,
+        NULL);  // render_view_host
+  }
+
+  void FailProvisionalLoad(MainFrame main_frame, ErrorType error_type) {
+    int net_error;
+
+    if (error_type == DNS_ERROR)
+      net_error = net::ERR_NAME_NOT_RESOLVED;
+    else
+      net_error = net::ERR_TIMED_OUT;
+
+    tab_helper_.DidFailProvisionalLoad(
+        1,  // frame id
+        (main_frame == MAIN_FRAME),
+        bogus_url_,  // validated_url
+        net_error,
+        string16(),
+        NULL);  // render_view_host
+  }
+
+  void FinishProbe(DnsProbeStatus status) {
+    tab_helper_.FinishProbe(status);
+  }
+
+  bool probe_running() { return tab_helper_.mock_probe_running(); }
+  DnsProbeStatus last_status_sent() { return tab_helper_.last_status_sent(); }
+  int sent_count() { return tab_helper_.mock_sent_count(); }
+
+ private:
+  MessageLoop message_loop_;
+  TestBrowserThread fake_ui_thread_;
+  TestNetErrorTabHelper tab_helper_;
+  GURL bogus_url_;
+};
+
+TEST_F(NetErrorTabHelperTest, Null) {
+  EXPECT_FALSE(probe_running());
+}
+
+TEST_F(NetErrorTabHelperTest, MainFrameNonDnsError) {
+  StartProvisionalLoad(MAIN_FRAME, NORMAL_PAGE);
+  FailProvisionalLoad(MAIN_FRAME, OTHER_ERROR);
+  EXPECT_FALSE(probe_running());
+  EXPECT_EQ(0, sent_count());
+}
+
+TEST_F(NetErrorTabHelperTest, NonMainFrameDnsError) {
+  StartProvisionalLoad(SUB_FRAME, NORMAL_PAGE);
+  FailProvisionalLoad(SUB_FRAME, DNS_ERROR);
+  EXPECT_FALSE(probe_running());
+  EXPECT_EQ(0, sent_count());
+}
+
+// Test complete DNS error page loads.  Note that the helper can see two error
+// page loads: Link Doctor loads an empty HTML page so the user knows something
+// is going on, then fails over to the normal error page if and when Link
+// Doctor fails to load or declines to provide a page.
+
+TEST_F(NetErrorTabHelperTest, ProbeResponseBeforeFirstCommit) {
+  StartProvisionalLoad(MAIN_FRAME, NORMAL_PAGE);
+  FailProvisionalLoad(MAIN_FRAME, DNS_ERROR);
+  EXPECT_TRUE(probe_running());
+  EXPECT_EQ(0, sent_count());
+
+  StartProvisionalLoad(MAIN_FRAME, ERROR_PAGE);
+  EXPECT_TRUE(probe_running());
+  EXPECT_EQ(0, sent_count());
+
+  FinishProbe(chrome_common_net::DNS_PROBE_FINISHED_NXDOMAIN);
+  EXPECT_FALSE(probe_running());
+  EXPECT_EQ(0, sent_count());
+
+  CommitProvisionalLoad(MAIN_FRAME);
+  EXPECT_FALSE(probe_running());
+  EXPECT_EQ(1, sent_count());
+  EXPECT_EQ(chrome_common_net::DNS_PROBE_FINISHED_NXDOMAIN, last_status_sent());
+
+  StartProvisionalLoad(MAIN_FRAME, ERROR_PAGE);
+  EXPECT_FALSE(probe_running());
+  EXPECT_EQ(1, sent_count());
+
+  CommitProvisionalLoad(MAIN_FRAME);
+  EXPECT_FALSE(probe_running());
+  EXPECT_EQ(2, sent_count());
+  EXPECT_EQ(chrome_common_net::DNS_PROBE_FINISHED_NXDOMAIN, last_status_sent());
+}
+
+TEST_F(NetErrorTabHelperTest, ProbeResponseBetweenFirstAndSecondCommit) {
+  StartProvisionalLoad(MAIN_FRAME, NORMAL_PAGE);
+  FailProvisionalLoad(MAIN_FRAME, DNS_ERROR);
+  EXPECT_TRUE(probe_running());
+  EXPECT_EQ(0, sent_count());
+
+  StartProvisionalLoad(MAIN_FRAME, ERROR_PAGE);
+  EXPECT_TRUE(probe_running());
+  EXPECT_EQ(0, sent_count());
+
+  CommitProvisionalLoad(MAIN_FRAME);
+  EXPECT_TRUE(probe_running());
+  EXPECT_EQ(1, sent_count());
+  EXPECT_EQ(chrome_common_net::DNS_PROBE_STARTED, last_status_sent());
+
+  FinishProbe(chrome_common_net::DNS_PROBE_FINISHED_NXDOMAIN);
+  EXPECT_FALSE(probe_running());
+  EXPECT_EQ(2, sent_count());
+  EXPECT_EQ(chrome_common_net::DNS_PROBE_FINISHED_NXDOMAIN, last_status_sent());
+
+  StartProvisionalLoad(MAIN_FRAME, ERROR_PAGE);
+  EXPECT_FALSE(probe_running());
+  EXPECT_EQ(2, sent_count());
+
+  CommitProvisionalLoad(MAIN_FRAME);
+  EXPECT_FALSE(probe_running());
+  EXPECT_EQ(3, sent_count());
+  EXPECT_EQ(chrome_common_net::DNS_PROBE_FINISHED_NXDOMAIN, last_status_sent());
+}
+
+TEST_F(NetErrorTabHelperTest, ProbeResponseAfterSecondCommit) {
+  StartProvisionalLoad(MAIN_FRAME, NORMAL_PAGE);
+  FailProvisionalLoad(MAIN_FRAME, DNS_ERROR);
+  EXPECT_TRUE(probe_running());
+  EXPECT_EQ(0, sent_count());
+
+  StartProvisionalLoad(MAIN_FRAME, ERROR_PAGE);
+  EXPECT_TRUE(probe_running());
+  EXPECT_EQ(0, sent_count());
+
+  CommitProvisionalLoad(MAIN_FRAME);
+  EXPECT_TRUE(probe_running());
+  EXPECT_EQ(1, sent_count());
+  EXPECT_EQ(chrome_common_net::DNS_PROBE_STARTED, last_status_sent());
+
+  StartProvisionalLoad(MAIN_FRAME, ERROR_PAGE);
+  EXPECT_TRUE(probe_running());
+  EXPECT_EQ(1, sent_count());
+
+  CommitProvisionalLoad(MAIN_FRAME);
+  EXPECT_TRUE(probe_running());
+  EXPECT_EQ(2, sent_count());
+  EXPECT_EQ(chrome_common_net::DNS_PROBE_STARTED, last_status_sent());
+
+  FinishProbe(chrome_common_net::DNS_PROBE_FINISHED_NXDOMAIN);
+  EXPECT_FALSE(probe_running());
+  EXPECT_EQ(3, sent_count());
+  EXPECT_EQ(chrome_common_net::DNS_PROBE_FINISHED_NXDOMAIN, last_status_sent());
+}
+
+// Send result even if a new page load has started; the error page is still
+// visible, and the user might cancel the load.
+TEST_F(NetErrorTabHelperTest, ProbeResponseAfterNewStart) {
+  StartProvisionalLoad(MAIN_FRAME, NORMAL_PAGE);
+  FailProvisionalLoad(MAIN_FRAME, DNS_ERROR);
+  EXPECT_TRUE(probe_running());
+  EXPECT_EQ(0, sent_count());
+
+  StartProvisionalLoad(MAIN_FRAME, ERROR_PAGE);
+  EXPECT_TRUE(probe_running());
+  EXPECT_EQ(0, sent_count());
+
+  CommitProvisionalLoad(MAIN_FRAME);
+  EXPECT_TRUE(probe_running());
+  EXPECT_EQ(1, sent_count());
+  EXPECT_EQ(chrome_common_net::DNS_PROBE_STARTED, last_status_sent());
+
+  StartProvisionalLoad(MAIN_FRAME, ERROR_PAGE);
+  EXPECT_TRUE(probe_running());
+  EXPECT_EQ(1, sent_count());
+
+  CommitProvisionalLoad(MAIN_FRAME);
+  EXPECT_TRUE(probe_running());
+  EXPECT_EQ(2, sent_count());
+  EXPECT_EQ(chrome_common_net::DNS_PROBE_STARTED, last_status_sent());
+
+  StartProvisionalLoad(MAIN_FRAME, NORMAL_PAGE);
+  EXPECT_TRUE(probe_running());
+  EXPECT_EQ(2, sent_count());
+
+  FinishProbe(chrome_common_net::DNS_PROBE_FINISHED_NXDOMAIN);
+  EXPECT_FALSE(probe_running());
+  EXPECT_EQ(3, sent_count());
+  EXPECT_EQ(chrome_common_net::DNS_PROBE_FINISHED_NXDOMAIN, last_status_sent());
+}
+
+// Don't send result if a new page has committed; the result would go to the
+// wrong page, and the error page is gone anyway.
+TEST_F(NetErrorTabHelperTest, ProbeResponseAfterNewCommit) {
+  StartProvisionalLoad(MAIN_FRAME, NORMAL_PAGE);
+  FailProvisionalLoad(MAIN_FRAME, DNS_ERROR);
+  EXPECT_TRUE(probe_running());
+  EXPECT_EQ(0, sent_count());
+
+  StartProvisionalLoad(MAIN_FRAME, ERROR_PAGE);
+  EXPECT_TRUE(probe_running());
+  EXPECT_EQ(0, sent_count());
+
+  CommitProvisionalLoad(MAIN_FRAME);
+  EXPECT_TRUE(probe_running());
+  EXPECT_EQ(1, sent_count());
+  EXPECT_EQ(chrome_common_net::DNS_PROBE_STARTED, last_status_sent());
+
+  StartProvisionalLoad(MAIN_FRAME, ERROR_PAGE);
+  EXPECT_TRUE(probe_running());
+  EXPECT_EQ(1, sent_count());
+
+  CommitProvisionalLoad(MAIN_FRAME);
+  EXPECT_TRUE(probe_running());
+  EXPECT_EQ(2, sent_count());
+  EXPECT_EQ(chrome_common_net::DNS_PROBE_STARTED, last_status_sent());
+
+  StartProvisionalLoad(MAIN_FRAME, NORMAL_PAGE);
+  EXPECT_TRUE(probe_running());
+  EXPECT_EQ(2, sent_count());
+
+  CommitProvisionalLoad(MAIN_FRAME);
+  EXPECT_TRUE(probe_running());
+  EXPECT_EQ(2, sent_count());
+
+  FinishProbe(chrome_common_net::DNS_PROBE_FINISHED_NXDOMAIN);
+  EXPECT_FALSE(probe_running());
+  EXPECT_EQ(2, sent_count());
+}
+
+TEST_F(NetErrorTabHelperTest, MultipleDnsErrorsWithProbesWithoutErrorPages) {
+  StartProvisionalLoad(MAIN_FRAME, NORMAL_PAGE);
+  FailProvisionalLoad(MAIN_FRAME, DNS_ERROR);
+  EXPECT_TRUE(probe_running());
+  EXPECT_EQ(0, sent_count());
+
+  FinishProbe(chrome_common_net::DNS_PROBE_FINISHED_NXDOMAIN);
+  EXPECT_FALSE(probe_running());
+  EXPECT_EQ(0, sent_count());
+
+  StartProvisionalLoad(MAIN_FRAME, NORMAL_PAGE);
+  FailProvisionalLoad(MAIN_FRAME, DNS_ERROR);
+  EXPECT_TRUE(probe_running());
+  EXPECT_EQ(0, sent_count());
+
+  FinishProbe(chrome_common_net::DNS_PROBE_FINISHED_NO_INTERNET);
+  EXPECT_FALSE(probe_running());
+  EXPECT_EQ(0, sent_count());
+}
+
+TEST_F(NetErrorTabHelperTest, MultipleDnsErrorsWithProbesAndErrorPages) {
+  StartProvisionalLoad(MAIN_FRAME, NORMAL_PAGE);
+  FailProvisionalLoad(MAIN_FRAME, DNS_ERROR);
+  EXPECT_TRUE(probe_running());
+  EXPECT_EQ(0, sent_count());
+
+  StartProvisionalLoad(MAIN_FRAME, ERROR_PAGE);
+  CommitProvisionalLoad(MAIN_FRAME);
+  EXPECT_TRUE(probe_running());
+  EXPECT_EQ(1, sent_count());
+  EXPECT_EQ(chrome_common_net::DNS_PROBE_STARTED, last_status_sent());
+
+  FinishProbe(chrome_common_net::DNS_PROBE_FINISHED_NXDOMAIN);
+  EXPECT_FALSE(probe_running());
+  EXPECT_EQ(2, sent_count());
+  EXPECT_EQ(chrome_common_net::DNS_PROBE_FINISHED_NXDOMAIN, last_status_sent());
+
+  StartProvisionalLoad(MAIN_FRAME, NORMAL_PAGE);
+  FailProvisionalLoad(MAIN_FRAME, DNS_ERROR);
+  EXPECT_TRUE(probe_running());
+  EXPECT_EQ(2, sent_count());
+
+  StartProvisionalLoad(MAIN_FRAME, ERROR_PAGE);
+  CommitProvisionalLoad(MAIN_FRAME);
+  EXPECT_TRUE(probe_running());
+  EXPECT_EQ(3, sent_count());
+  EXPECT_EQ(chrome_common_net::DNS_PROBE_STARTED, last_status_sent());
+
+  FinishProbe(chrome_common_net::DNS_PROBE_FINISHED_NO_INTERNET);
+  EXPECT_FALSE(probe_running());
+  EXPECT_EQ(4, sent_count());
+  EXPECT_EQ(chrome_common_net::DNS_PROBE_FINISHED_NO_INTERNET,
+            last_status_sent());
+}
+
+// If multiple DNS errors occur in a row before a probe result, don't start
+// multiple probes.
+TEST_F(NetErrorTabHelperTest, CoalesceFailures) {
+  StartProvisionalLoad(MAIN_FRAME, NORMAL_PAGE);
+  FailProvisionalLoad(MAIN_FRAME, DNS_ERROR);
+  StartProvisionalLoad(MAIN_FRAME, ERROR_PAGE);
+  CommitProvisionalLoad(MAIN_FRAME);
+  EXPECT_TRUE(probe_running());
+  EXPECT_EQ(1, sent_count());
+  EXPECT_EQ(chrome_common_net::DNS_PROBE_STARTED, last_status_sent());
+
+  StartProvisionalLoad(MAIN_FRAME, NORMAL_PAGE);
+  FailProvisionalLoad(MAIN_FRAME, DNS_ERROR);
+  StartProvisionalLoad(MAIN_FRAME, ERROR_PAGE);
+  CommitProvisionalLoad(MAIN_FRAME);
+  EXPECT_TRUE(probe_running());
+  EXPECT_EQ(2, sent_count());
+  EXPECT_EQ(chrome_common_net::DNS_PROBE_STARTED, last_status_sent());
+
+  StartProvisionalLoad(MAIN_FRAME, NORMAL_PAGE);
+  FailProvisionalLoad(MAIN_FRAME, DNS_ERROR);
+  StartProvisionalLoad(MAIN_FRAME, ERROR_PAGE);
+  CommitProvisionalLoad(MAIN_FRAME);
+  EXPECT_TRUE(probe_running());
+  EXPECT_EQ(3, sent_count());
+  EXPECT_EQ(chrome_common_net::DNS_PROBE_STARTED, last_status_sent());
+
+  FinishProbe(chrome_common_net::DNS_PROBE_FINISHED_NXDOMAIN);
+  EXPECT_FALSE(probe_running());
+  EXPECT_EQ(4, sent_count());
+  EXPECT_EQ(chrome_common_net::DNS_PROBE_FINISHED_NXDOMAIN, last_status_sent());
+}
diff --git a/chrome/chrome_browser.gypi b/chrome/chrome_browser.gypi
index fd97650..618e0a8 100644
--- a/chrome/chrome_browser.gypi
+++ b/chrome/chrome_browser.gypi
@@ -1095,8 +1095,8 @@
         'browser/net/connection_tester.h',
         'browser/net/crl_set_fetcher.cc',
         'browser/net/crl_set_fetcher.h',
-        'browser/net/dns_probe_job.cc',
-        'browser/net/dns_probe_job.h',
+        'browser/net/dns_probe_runner.cc',
+        'browser/net/dns_probe_runner.h',
         'browser/net/dns_probe_service.cc',
         'browser/net/dns_probe_service.h',
         'browser/net/evicted_domain_cookie_counter.cc',
diff --git a/chrome/chrome_common.gypi b/chrome/chrome_common.gypi
index a9b5d56..1f72cee 100644
--- a/chrome/chrome_common.gypi
+++ b/chrome/chrome_common.gypi
@@ -729,8 +729,8 @@
       'target_name': 'common_net',
       'type': 'static_library',
       'sources': [
-        'common/net/net_error_tracker.cc',
-        'common/net/net_error_tracker.h',
+        'common/net/net_error_info.cc',
+        'common/net/net_error_info.h',
         'common/net/net_resource_provider.cc',
         'common/net/net_resource_provider.h',
         'common/net/predictor_common.h',
diff --git a/chrome/chrome_tests.gypi b/chrome/chrome_tests.gypi
index 34470b6..fa669016 100644
--- a/chrome/chrome_tests.gypi
+++ b/chrome/chrome_tests.gypi
@@ -1454,6 +1454,7 @@
         'browser/media_galleries/media_galleries_dialog_controller_mock.h',
         'browser/metrics/metrics_service_browsertest.cc',
         'browser/net/cookie_policy_browsertest.cc',
+        'browser/net/dns_probe_browsertest.cc',
         'browser/net/ftp_browsertest.cc',
         'browser/net/load_timing_browsertest.cc',
         'browser/net/predictor_browsertest.cc',
diff --git a/chrome/chrome_tests_unit.gypi b/chrome/chrome_tests_unit.gypi
index 95e3f54..a78d569 100644
--- a/chrome/chrome_tests_unit.gypi
+++ b/chrome/chrome_tests_unit.gypi
@@ -134,6 +134,8 @@
         'browser/google_apis/test_util.h',
         'browser/media_galleries/media_galleries_test_util.cc',
         'browser/media_galleries/media_galleries_test_util.h',
+        'browser/net/dns_probe_test_util.cc',
+        'browser/net/dns_probe_test_util.h',
         'browser/net/url_request_mock_util.cc',
         'browser/net/url_request_mock_util.h',
         'browser/notifications/notification_test_util.cc',
@@ -969,12 +971,13 @@
         'browser/net/chrome_fraudulent_certificate_reporter_unittest.cc',
         'browser/net/chrome_network_delegate_unittest.cc',
         'browser/net/connection_tester_unittest.cc',
-        'browser/net/dns_probe_job_unittest.cc',
+        'browser/net/dns_probe_runner_unittest.cc',
         'browser/net/dns_probe_service_unittest.cc',
         'browser/net/evicted_domain_cookie_counter_unittest.cc',
         'browser/net/gaia/gaia_oauth_fetcher_unittest.cc',
         'browser/net/http_pipelining_compatibility_client_unittest.cc',
         'browser/net/http_server_properties_manager_unittest.cc',
+        'browser/net/net_error_tab_helper_unittest.cc',
         'browser/net/net_log_temp_file_unittest.cc',
         'browser/net/network_stats_unittest.cc',
         'browser/net/network_time_tracker_unittest.cc',
@@ -1722,7 +1725,6 @@
         'common/metrics/metrics_util_unittest.cc',
         'common/metrics/variations/variations_util_unittest.cc',
         'common/multi_process_lock_unittest.cc',
-        'common/net/net_error_tracker_unittest.cc',
         'common/net/x509_certificate_model_unittest.cc',
         'common/partial_circular_buffer_unittest.cc',
         'common/policy/policy_schema_unittest.cc',
@@ -1747,6 +1749,7 @@
         'renderer/extensions/renderer_permissions_policy_delegate_unittest.cc',
         'renderer/extensions/safe_builtins_unittest.cc',
         'renderer/media/chrome_webrtc_log_message_delegate_unittest.cc',
+        'renderer/net/net_error_helper_unittest.cc',
         'renderer/net/predictor_queue_unittest.cc',
         'renderer/net/renderer_predictor_unittest.cc',
         'renderer/plugins/plugin_uma_unittest.cc',
diff --git a/chrome/common/localized_error.cc b/chrome/common/localized_error.cc
index d23b1b4..136607a 100644
--- a/chrome/common/localized_error.cc
+++ b/chrome/common/localized_error.cc
@@ -15,6 +15,7 @@
 #include "chrome/common/extensions/extension_icon_set.h"
 #include "chrome/common/extensions/extension_set.h"
 #include "chrome/common/extensions/manifest_handlers/icons_handler.h"
+#include "chrome/common/net/net_error_info.h"
 #include "grit/chromium_strings.h"
 #include "grit/generated_resources.h"
 #include "net/base/escape.h"
@@ -369,6 +370,53 @@ const LocalizedErrorMap http_error_options[] = {
   },
 };
 
+const LocalizedErrorMap dns_probe_error_options[] = {
+  {chrome_common_net::DNS_PROBE_POSSIBLE,
+   IDS_ERRORPAGES_TITLE_NOT_AVAILABLE,
+   IDS_ERRORPAGES_HEADING_NOT_AVAILABLE,
+   IDS_ERRORPAGES_SUMMARY_DNS_PROBE_RUNNING,
+   IDS_ERRORPAGES_DETAILS_DNS_PROBE_RUNNING,
+   SUGGEST_RELOAD,
+  },
+
+  // DNS_PROBE_NOT_RUN is not here; NetErrorHelper will restore the original
+  // error, which might be one of several DNS-related errors.
+
+  {chrome_common_net::DNS_PROBE_STARTED,
+   IDS_ERRORPAGES_TITLE_NOT_AVAILABLE,
+   IDS_ERRORPAGES_HEADING_NOT_AVAILABLE,
+   IDS_ERRORPAGES_SUMMARY_DNS_PROBE_RUNNING,
+   IDS_ERRORPAGES_DETAILS_DNS_PROBE_RUNNING,
+   // Include SUGGEST_RELOAD so the More button doesn't jump when we update.
+   SUGGEST_RELOAD,
+  },
+
+  // DNS_PROBE_FINISHED_UNKNOWN is not here; NetErrorHelper will restore the
+  // original error, which might be one of several DNS-related errors.
+
+  {chrome_common_net::DNS_PROBE_FINISHED_NO_INTERNET,
+   IDS_ERRORPAGES_TITLE_NOT_AVAILABLE,
+   IDS_ERRORPAGES_HEADING_NOT_AVAILABLE,
+   IDS_ERRORPAGES_SUMMARY_INTERNET_DISCONNECTED,
+   IDS_ERRORPAGES_DETAILS_INTERNET_DISCONNECTED,
+   SUGGEST_RELOAD | SUGGEST_CHECK_CONNECTION | SUGGEST_FIREWALL_CONFIG,
+  },
+  {chrome_common_net::DNS_PROBE_FINISHED_BAD_CONFIG,
+   IDS_ERRORPAGES_TITLE_NOT_AVAILABLE,
+   IDS_ERRORPAGES_HEADING_NOT_AVAILABLE,
+   IDS_ERRORPAGES_SUMMARY_NAME_NOT_RESOLVED,
+   IDS_ERRORPAGES_DETAILS_NAME_NOT_RESOLVED,
+   SUGGEST_RELOAD | SUGGEST_DNS_CONFIG | SUGGEST_FIREWALL_CONFIG,
+  },
+  {chrome_common_net::DNS_PROBE_FINISHED_NXDOMAIN,
+   IDS_ERRORPAGES_TITLE_NOT_AVAILABLE,
+   IDS_ERRORPAGES_HEADING_NOT_AVAILABLE,
+   IDS_ERRORPAGES_SUMMARY_NAME_NOT_RESOLVED,
+   IDS_ERRORPAGES_DETAILS_NAME_NOT_RESOLVED,
+   SUGGEST_RELOAD,
+  },
+};
+
 const LocalizedErrorMap* FindErrorMapInArray(const LocalizedErrorMap* maps,
                                                    size_t num_maps,
                                                    int error_code) {
@@ -393,6 +441,13 @@ const LocalizedErrorMap* LookupErrorMap(const std::string& error_domain,
     return FindErrorMapInArray(http_error_options,
                                arraysize(http_error_options),
                                error_code);
+  } else if (error_domain == chrome_common_net::kDnsProbeErrorDomain) {
+    const LocalizedErrorMap* map =
+        FindErrorMapInArray(dns_probe_error_options,
+                            arraysize(dns_probe_error_options),
+                            error_code);
+    DCHECK(map);
+    return map;
   } else {
     NOTREACHED();
     return NULL;
@@ -502,6 +557,10 @@ void LocalizedError::GetStrings(const WebKit::WebURLError& error,
     // Remove the leading "net::" from the returned string.
     RemoveChars(ascii_error_string, "net:", &ascii_error_string);
     error_string = ASCIIToUTF16(ascii_error_string);
+  } else if (error_domain == chrome_common_net::kDnsProbeErrorDomain) {
+    std::string ascii_error_string =
+        chrome_common_net::DnsProbeStatusToString(error_code);
+    error_string = ASCIIToUTF16(ascii_error_string);
   } else {
     DCHECK_EQ(LocalizedError::kHttpErrorDomain, error_domain);
     error_string = base::IntToString16(error_code);
diff --git a/chrome/common/net/net_error_info.cc b/chrome/common/net/net_error_info.cc
new file mode 100644
index 0000000..e350b89
--- /dev/null
+++ b/chrome/common/net/net_error_info.cc
@@ -0,0 +1,48 @@
+// Copyright 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "base/logging.h"
+#include "base/metrics/field_trial.h"
+#include "chrome/common/net/net_error_info.h"
+
+namespace chrome_common_net {
+
+const char kDnsProbeErrorDomain[] = "dnsprobe";
+
+const char* DnsProbeStatusToString(int status) {
+  switch (status) {
+  case DNS_PROBE_POSSIBLE:
+    return "DNS_PROBE_POSSIBLE";
+  case DNS_PROBE_NOT_RUN:
+    return "DNS_PROBE_NOT_RUN";
+  case DNS_PROBE_STARTED:
+    return "DNS_PROBE_STARTED";
+  case DNS_PROBE_FINISHED_INCONCLUSIVE:
+    return "DNS_PROBE_FINISHED_INCONCLUSIVE";
+  case DNS_PROBE_FINISHED_NO_INTERNET:
+    return "DNS_PROBE_FINISHED_NO_INTERNET";
+  case DNS_PROBE_FINISHED_BAD_CONFIG:
+    return "DNS_PROBE_FINISHED_BAD_CONFIG";
+  case DNS_PROBE_FINISHED_NXDOMAIN:
+    return "DNS_PROBE_FINISHED_NXDOMAIN";
+  default:
+    NOTREACHED();
+    return "";
+  }
+}
+
+bool DnsProbeStatusIsFinished(DnsProbeStatus status) {
+  return status >= DNS_PROBE_FINISHED_INCONCLUSIVE &&
+         status < DNS_PROBE_MAX;
+}
+
+bool DnsProbesEnabledByFieldTrial() {
+  const char kDnsProbeFieldTrialName[] = "DnsProbe-Enable";
+  const char kDnsProbeFieldTrialEnableGroupName[] = "enable";
+
+  return base::FieldTrialList::FindFullName(kDnsProbeFieldTrialName) ==
+         kDnsProbeFieldTrialEnableGroupName;
+}
+
+}  // namespace chrome_common_net
diff --git a/chrome/common/net/net_error_info.h b/chrome/common/net/net_error_info.h
index 9f8d08a..ec9d816 100644
--- a/chrome/common/net/net_error_info.h
+++ b/chrome/common/net/net_error_info.h
@@ -7,14 +7,69 @@
 
 namespace chrome_common_net {
 
-enum DnsProbeResult {
-  DNS_PROBE_UNKNOWN,
-  DNS_PROBE_NO_INTERNET,
-  DNS_PROBE_BAD_CONFIG,
-  DNS_PROBE_NXDOMAIN,
+// The status of a DNS probe that the NetErrorTabHelper may or may not have
+// started.
+//
+// The DNS_PROBE_FINISHED_* values are used in histograms, so:
+// 1. FINISHED_UNKNOWN must remain the first FINISHED_* value.
+// 2. FINISHED_* values must not be rearranged relative to FINISHED_UNKNOWN.
+// 3. New FINISHED_* values must be inserted at the end.
+// 4. New non-FINISHED_* values must be inserted before FINISHED_UNKNOWN.
+enum DnsProbeStatus {
+  // A DNS probe may be run for this error page.  (This status is only used on
+  // the renderer side before it's received a status update from the browser.)
+  DNS_PROBE_POSSIBLE,
+
+  // A DNS probe will not be run for this error page.  (This happens if the
+  // user has the "Use web service to resolve navigation errors" preference
+  // turned off, or if probes are disabled by the field trial.)
+  DNS_PROBE_NOT_RUN,
+
+  // A DNS probe has been started for this error page.  The renderer should
+  // expect to receive another IPC with one of the FINISHED statuses once the
+  // probe has finished (as long as the error page is still loaded).
+  DNS_PROBE_STARTED,
+
+  // A DNS probe has finished with one of the following results:
+
+  // The probe was inconclusive.
+  DNS_PROBE_FINISHED_INCONCLUSIVE,
+
+  // There's no internet connection.
+  DNS_PROBE_FINISHED_NO_INTERNET,
+
+  // The DNS configuration is wrong, or the servers are down or broken.
+  DNS_PROBE_FINISHED_BAD_CONFIG,
+
+  // The DNS servers are working fine, so the domain must not exist.
+  DNS_PROBE_FINISHED_NXDOMAIN,
+
   DNS_PROBE_MAX
 };
 
+// Returns a string representing |status|.  It should be simply the name of
+// the value as a string, but don't rely on that.  This is presented to the
+// user as part of the DNS error page (as the error code, at the bottom),
+// and is also used in some verbose log messages.
+//
+// |status| is an int because error codes are ints by the time they get to the
+// localized error system, and we don't want to require the caller to cast back
+// to a probe status.  The function will NOTREACHED() and return an empty
+// string if given an int that does not match a value in DnsProbeStatus (or if
+// it is DNS_PROBE_MAX, which is not a real status).
+const char* DnsProbeStatusToString(int status);
+
+// Returns true if |status| is one of the DNS_PROBE_FINISHED_* statuses.
+bool DnsProbeStatusIsFinished(DnsProbeStatus status);
+
+// Returns true if DNS probes are enabled (by the DnsProbe-Enable field trial),
+// or false if they are disabled or the field trial wasn't found.
+bool DnsProbesEnabledByFieldTrial();
+
+// The error domain used to pass DNS probe statuses to the localized error
+// code.
+extern const char kDnsProbeErrorDomain[];
+
 }  // namespace chrome_common_net
 
 #endif  // CHROME_COMMON_NET_NET_ERROR_INFO_H_
diff --git a/chrome/common/net/net_error_tracker.cc b/chrome/common/net/net_error_tracker.cc
deleted file mode 100644
index 6cf69ca..0000000
--- a/chrome/common/net/net_error_tracker.cc
+++ /dev/null
@@ -1,66 +0,0 @@
-// Copyright (c) 2013 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#include "chrome/common/net/net_error_tracker.h"
-
-NetErrorTracker::NetErrorTracker(const Callback& callback)
-    : callback_(callback),
-      load_state_(LOAD_NONE),
-      load_type_(PAGE_NORMAL),
-      error_type_(ERROR_OTHER),
-      dns_error_page_state_(DNS_ERROR_PAGE_NONE) {
-}
-
-NetErrorTracker::~NetErrorTracker() {
-}
-
-void NetErrorTracker::OnStartProvisionalLoad(FrameType frame, PageType page) {
-  if (frame == FRAME_SUB)
-    return;
-
-  load_state_ = LOAD_STARTED;
-  load_type_ = page;
-
-  // TODO(ttuttle): Add support for aborts, then move this to OnCommit.
-  if (load_type_ == PAGE_NORMAL)
-    SetDnsErrorPageState(DNS_ERROR_PAGE_NONE);
-}
-
-void NetErrorTracker::OnCommitProvisionalLoad(FrameType frame) {
-  if (frame == FRAME_SUB)
-    return;
-
-  load_state_ = LOAD_COMMITTED;
-}
-
-void NetErrorTracker::OnFailProvisionalLoad(FrameType frame, ErrorType error) {
-  if (frame == FRAME_SUB)
-    return;
-
-  load_state_ = LOAD_FAILED;
-
-  if (load_type_ == PAGE_NORMAL) {
-    error_type_ = error;
-    if (error_type_ == ERROR_DNS)
-      SetDnsErrorPageState(DNS_ERROR_PAGE_PENDING);
-  }
-}
-
-void NetErrorTracker::OnFinishLoad(FrameType frame) {
-  if (frame == FRAME_SUB)
-    return;
-
-  load_state_ = LOAD_FINISHED;
-
-  if (load_type_ == PAGE_ERROR && error_type_ == ERROR_DNS)
-    SetDnsErrorPageState(DNS_ERROR_PAGE_LOADED);
-}
-
-void NetErrorTracker::SetDnsErrorPageState(DnsErrorPageState state) {
-  if (state == dns_error_page_state_)
-    return;
-
-  dns_error_page_state_ = state;
-  callback_.Run(state);
-}
diff --git a/chrome/common/net/net_error_tracker.h b/chrome/common/net/net_error_tracker.h
deleted file mode 100644
index 530abcb..0000000
--- a/chrome/common/net/net_error_tracker.h
+++ /dev/null
@@ -1,66 +0,0 @@
-// Copyright (c) 2013 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#ifndef CHROME_COMMON_NET_NET_ERROR_TRACKER_H_
-#define CHROME_COMMON_NET_NET_ERROR_TRACKER_H_
-
-#include "base/bind.h"
-
-class NetErrorTracker {
- public:
-  enum FrameType {
-    FRAME_SUB,
-    FRAME_MAIN
-  };
-
-  enum PageType {
-    PAGE_NORMAL,
-    PAGE_ERROR
-  };
-
-  enum ErrorType {
-    ERROR_OTHER,
-    ERROR_DNS
-  };
-
-  enum DnsErrorPageState {
-    DNS_ERROR_PAGE_NONE,
-    DNS_ERROR_PAGE_PENDING,
-    DNS_ERROR_PAGE_LOADED
-  };
-
-  typedef base::Callback<void(DnsErrorPageState state)> Callback;
-
-  explicit NetErrorTracker(const Callback& callback);
-  ~NetErrorTracker();
-
-  void OnStartProvisionalLoad(FrameType frame, PageType page);
-  void OnCommitProvisionalLoad(FrameType frame);
-  void OnFailProvisionalLoad(FrameType frame, ErrorType error);
-  void OnFinishLoad(FrameType frame);
-
- private:
-  enum LoadState {
-    LOAD_NONE,
-    LOAD_STARTED,
-    LOAD_COMMITTED,
-    LOAD_FAILED,
-    LOAD_FINISHED
-  };
-
-  void SetDnsErrorPageState(DnsErrorPageState state);
-
-  Callback callback_;
-
-  LoadState load_state_;
-  PageType load_type_;
-
-  ErrorType error_type_;
-
-  DnsErrorPageState dns_error_page_state_;
-
-  DISALLOW_COPY_AND_ASSIGN(NetErrorTracker);
-};
-
-#endif  // CHROME_COMMON_NET_NET_ERROR_TRACKER_H_
diff --git a/chrome/common/net/net_error_tracker_unittest.cc b/chrome/common/net/net_error_tracker_unittest.cc
deleted file mode 100644
index 7253deb..0000000
--- a/chrome/common/net/net_error_tracker_unittest.cc
+++ /dev/null
@@ -1,98 +0,0 @@
-// Copyright (c) 2013 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#include "chrome/common/net/net_error_tracker.h"
-
-#include "testing/gtest/include/gtest/gtest.h"
-
-namespace {
-
-typedef NetErrorTracker::FrameType FrameType;
-typedef NetErrorTracker::PageType PageType;
-typedef NetErrorTracker::ErrorType ErrorType;
-
-const FrameType FRAME_SUB = NetErrorTracker::FRAME_SUB;
-const FrameType FRAME_MAIN = NetErrorTracker::FRAME_MAIN;
-
-const PageType PAGE_NORMAL = NetErrorTracker::PAGE_NORMAL;
-const PageType PAGE_ERROR = NetErrorTracker::PAGE_ERROR;
-
-const ErrorType ERROR_OTHER = NetErrorTracker::ERROR_OTHER;
-const ErrorType ERROR_DNS = NetErrorTracker::ERROR_DNS;
-
-class NetErrorTrackerTest : public testing::Test {
- public:
-  NetErrorTrackerTest()
-      : tracker_(base::Bind(&NetErrorTrackerTest::TrackerCallback,
-                            base::Unretained(this))),
-        callback_state_(NetErrorTracker::DNS_ERROR_PAGE_NONE),
-        callback_count_(0) {
-  }
-
- protected:
-  NetErrorTracker tracker_;
-  NetErrorTracker::DnsErrorPageState callback_state_;
-  int callback_count_;
-
- private:
-  void TrackerCallback(NetErrorTracker::DnsErrorPageState state) {
-    callback_state_ = state;
-    ++callback_count_;
-  }
-};
-
-TEST_F(NetErrorTrackerTest, InitialState) {
-  EXPECT_EQ(0, callback_count_);
-  EXPECT_EQ(NetErrorTracker::DNS_ERROR_PAGE_NONE, callback_state_);
-}
-
-TEST_F(NetErrorTrackerTest, SuccessfulMainFrameLoad) {
-  tracker_.OnStartProvisionalLoad(FRAME_MAIN, PAGE_NORMAL);
-  tracker_.OnCommitProvisionalLoad(FRAME_MAIN);
-  tracker_.OnFinishLoad(FRAME_MAIN);
-
-  EXPECT_EQ(0, callback_count_);
-  EXPECT_EQ(NetErrorTracker::DNS_ERROR_PAGE_NONE, callback_state_);
-}
-
-TEST_F(NetErrorTrackerTest, SuccessfulSubFrameLoad) {
-  tracker_.OnStartProvisionalLoad(FRAME_SUB, PAGE_NORMAL);
-  tracker_.OnCommitProvisionalLoad(FRAME_SUB);
-  tracker_.OnFinishLoad(FRAME_SUB);
-
-  EXPECT_EQ(0, callback_count_);
-  EXPECT_EQ(NetErrorTracker::DNS_ERROR_PAGE_NONE, callback_state_);
-}
-
-TEST_F(NetErrorTrackerTest, FailedMainFrameLoad) {
-  tracker_.OnStartProvisionalLoad(FRAME_MAIN, PAGE_NORMAL);
-  EXPECT_EQ(0, callback_count_);
-  EXPECT_EQ(NetErrorTracker::DNS_ERROR_PAGE_NONE, callback_state_);
-
-  tracker_.OnFailProvisionalLoad(FRAME_MAIN, ERROR_DNS);
-  EXPECT_EQ(1, callback_count_);
-  EXPECT_EQ(NetErrorTracker::DNS_ERROR_PAGE_PENDING, callback_state_);
-
-  tracker_.OnStartProvisionalLoad(FRAME_MAIN, PAGE_ERROR);
-  tracker_.OnCommitProvisionalLoad(FRAME_MAIN);
-  tracker_.OnFinishLoad(FRAME_MAIN);
-  EXPECT_EQ(2, callback_count_);
-  EXPECT_EQ(NetErrorTracker::DNS_ERROR_PAGE_LOADED, callback_state_);
-
-  tracker_.OnStartProvisionalLoad(FRAME_MAIN, PAGE_NORMAL);
-  EXPECT_EQ(3, callback_count_);
-  EXPECT_EQ(NetErrorTracker::DNS_ERROR_PAGE_NONE, callback_state_);
-}
-
-TEST_F(NetErrorTrackerTest, FailedSubFrameLoad) {
-  tracker_.OnStartProvisionalLoad(FRAME_SUB, PAGE_NORMAL);
-  tracker_.OnFailProvisionalLoad(FRAME_SUB, ERROR_DNS);
-  tracker_.OnStartProvisionalLoad(FRAME_SUB, PAGE_ERROR);
-  tracker_.OnCommitProvisionalLoad(FRAME_SUB);
-  tracker_.OnFinishLoad(FRAME_SUB);
-  EXPECT_EQ(0, callback_count_);
-  EXPECT_EQ(NetErrorTracker::DNS_ERROR_PAGE_NONE, callback_state_);
-}
-
-}  // namespace
diff --git a/chrome/common/render_messages.h b/chrome/common/render_messages.h
index fc065fb..fee44d6 100644
--- a/chrome/common/render_messages.h
+++ b/chrome/common/render_messages.h
@@ -381,7 +381,7 @@ IPC_MESSAGE_ROUTED0(ChromeViewMsg_SetAsInterstitial)
 // NetErrorHelper will receive this mesage and replace or update the error
 // page with more specific troubleshooting suggestions.
 IPC_MESSAGE_ROUTED1(ChromeViewMsg_NetErrorInfo,
-                    int /* DNS probe result */)
+                    int /* DNS probe status */)
 
 //-----------------------------------------------------------------------------
 // Misc messages
diff --git a/chrome/renderer/chrome_content_renderer_client.cc b/chrome/renderer/chrome_content_renderer_client.cc
index 45f9029..79d57a7 100644
--- a/chrome/renderer/chrome_content_renderer_client.cc
+++ b/chrome/renderer/chrome_content_renderer_client.cc
@@ -849,7 +849,7 @@ bool ChromeContentRendererClient::HasErrorPage(int http_status_code,
 }
 
 void ChromeContentRendererClient::GetNavigationErrorStrings(
-    WebKit::WebFrame* /* frame */,
+    WebKit::WebFrame* frame,
     const WebKit::WebURLRequest& failed_request,
     const WebKit::WebURLError& error,
     std::string* error_html,
@@ -877,11 +877,13 @@ void ChromeContentRendererClient::GetNavigationErrorStrings(
       // error messages?
       resource_id = IDR_ERROR_APP_HTML;
     } else {
-      LocalizedError::GetStrings(
-          error,
-          is_post,
-          RenderThread::Get()->GetLocale(),
-          &error_strings);
+      const std::string locale = RenderThread::Get()->GetLocale();
+      if (!NetErrorHelper::GetErrorStringsForDnsProbe(
+              frame, error, is_post, locale, &error_strings)) {
+        // In most cases, the NetErrorHelper won't provide DNS-probe-specific
+        // error pages, so fall back to LocalizedError.
+        LocalizedError::GetStrings(error, is_post, locale, &error_strings);
+      }
       resource_id = IDR_NET_ERROR_HTML;
     }
 
diff --git a/chrome/renderer/net/net_error_helper.cc b/chrome/renderer/net/net_error_helper.cc
index d73386d..46a8e0e 100644
--- a/chrome/renderer/net/net_error_helper.cc
+++ b/chrome/renderer/net/net_error_helper.cc
@@ -4,6 +4,10 @@
 
 #include "chrome/renderer/net/net_error_helper.h"
 
+#include <string>
+
+#include "base/json/json_writer.h"
+#include "base/strings/utf_string_conversions.h"
 #include "base/values.h"
 #include "chrome/common/localized_error.h"
 #include "chrome/common/net/net_error_info.h"
@@ -17,13 +21,16 @@
 #include "ipc/ipc_message_macros.h"
 #include "net/base/net_errors.h"
 #include "third_party/WebKit/public/platform/WebURL.h"
-#include "third_party/WebKit/public/platform/WebURLError.h"
 #include "third_party/WebKit/public/platform/WebURLRequest.h"
 #include "third_party/WebKit/public/web/WebDataSource.h"
 #include "third_party/WebKit/public/web/WebFrame.h"
 #include "url/gurl.h"
 
-using chrome_common_net::DnsProbeResult;
+using base::JSONWriter;
+using chrome_common_net::DnsProbeStatus;
+using chrome_common_net::DnsProbeStatusIsFinished;
+using chrome_common_net::DnsProbeStatusToString;
+using chrome_common_net::DnsProbesEnabledByFieldTrial;
 using content::RenderThread;
 using content::RenderView;
 using content::RenderViewObserver;
@@ -31,75 +38,31 @@ using content::kUnreachableWebDataURL;
 
 namespace {
 
-GURL GetProvisionallyLoadingURLFromWebFrame(WebKit::WebFrame* frame) {
-  return frame->provisionalDataSource()->request().url();
+bool IsLoadingErrorPage(WebKit::WebFrame* frame) {
+  GURL url = frame->provisionalDataSource()->request().url();
+  return url.spec() == kUnreachableWebDataURL;
 }
 
-bool IsErrorPage(const GURL& url) {
-  return (url.spec() == kUnreachableWebDataURL);
+bool IsMainFrame(const WebKit::WebFrame* frame) {
+  return !frame->parent();
 }
 
 // Returns whether |net_error| is a DNS-related error (and therefore whether
 // the tab helper should start a DNS probe after receiving it.)
-bool IsDnsError(int net_error) {
-  return net_error == net::ERR_NAME_NOT_RESOLVED ||
-         net_error == net::ERR_NAME_RESOLUTION_FAILED;
-}
-
-NetErrorTracker::FrameType GetFrameType(WebKit::WebFrame* frame) {
-  return frame->parent() ? NetErrorTracker::FRAME_SUB
-                         : NetErrorTracker::FRAME_MAIN;
-}
-
-NetErrorTracker::PageType GetPageType(WebKit::WebFrame* frame) {
-  bool error_page = IsErrorPage(GetProvisionallyLoadingURLFromWebFrame(frame));
-  return error_page ? NetErrorTracker::PAGE_ERROR
-                    : NetErrorTracker::PAGE_NORMAL;
-}
-
-NetErrorTracker::ErrorType GetErrorType(const WebKit::WebURLError& error) {
-  return IsDnsError(error.reason) ? NetErrorTracker::ERROR_DNS
-                                  : NetErrorTracker::ERROR_OTHER;
-}
-
-// Converts a DNS probe result into a net error.  Returns OK if the error page
-// should not be changed from the original DNS error.
-int DnsProbeResultToNetError(DnsProbeResult result) {
-  switch (result) {
-  case chrome_common_net::DNS_PROBE_UNKNOWN:
-    return net::OK;
-  case chrome_common_net::DNS_PROBE_NO_INTERNET:
-    // TODO(ttuttle): This is not the same error as when NCN returns this;
-    // ideally we should have two separate error codes for "no network" and
-    // "network with no internet".
-    return net::ERR_INTERNET_DISCONNECTED;
-  case chrome_common_net::DNS_PROBE_BAD_CONFIG:
-    // This is unspecific enough that we should still show the full DNS error
-    // page.
-    return net::OK;
-  case chrome_common_net::DNS_PROBE_NXDOMAIN:
-    return net::ERR_NAME_NOT_RESOLVED;
-  default:
-    NOTREACHED();
-    return net::OK;
-  }
-}
-
-WebKit::WebURLError NetErrorToWebURLError(int net_error) {
-  WebKit::WebURLError error;
-  error.domain = WebKit::WebString::fromUTF8(net::kErrorDomain);
-  error.reason = net_error;
-  return error;
+bool IsDnsError(const WebKit::WebURLError& error) {
+  return std::string(error.domain.utf8()) == net::kErrorDomain &&
+         (error.reason == net::ERR_NAME_NOT_RESOLVED ||
+          error.reason == net::ERR_NAME_RESOLUTION_FAILED);
 }
 
 }  // namespace
 
 NetErrorHelper::NetErrorHelper(RenderView* render_view)
     : RenderViewObserver(render_view),
-      tracker_(base::Bind(&NetErrorHelper::TrackerCallback,
-                          base::Unretained(this))),
-      dns_error_page_state_(NetErrorTracker::DNS_ERROR_PAGE_NONE),
-      updated_error_page_(false),
+      last_probe_status_(chrome_common_net::DNS_PROBE_POSSIBLE),
+      last_start_was_error_page_(false),
+      last_fail_was_dns_error_(false),
+      forwarding_probe_results_(false),
       is_failed_post_(false) {
 }
 
@@ -107,84 +70,185 @@ NetErrorHelper::~NetErrorHelper() {
 }
 
 void NetErrorHelper::DidStartProvisionalLoad(WebKit::WebFrame* frame) {
-  tracker_.OnStartProvisionalLoad(GetFrameType(frame), GetPageType(frame));
+  OnStartLoad(IsMainFrame(frame), IsLoadingErrorPage(frame));
 }
 
 void NetErrorHelper::DidFailProvisionalLoad(WebKit::WebFrame* frame,
                                             const WebKit::WebURLError& error) {
-  WebKit::WebDataSource* data_source = frame->provisionalDataSource();
-  const WebKit::WebURLRequest& failed_request = data_source->request();
-  is_failed_post_ = EqualsASCII(failed_request.httpMethod(), "POST");
-  tracker_.OnFailProvisionalLoad(GetFrameType(frame), GetErrorType(error));
+  const bool main_frame = IsMainFrame(frame);
+  const bool dns_error = IsDnsError(error);
+
+  OnFailLoad(main_frame, dns_error);
+
+  if (main_frame && dns_error) {
+    last_error_ = error;
+
+    WebKit::WebDataSource* data_source = frame->provisionalDataSource();
+    const WebKit::WebURLRequest& failed_request = data_source->request();
+    is_failed_post_ = EqualsASCII(failed_request.httpMethod(), "POST");
+  }
 }
 
 void NetErrorHelper::DidCommitProvisionalLoad(WebKit::WebFrame* frame,
                                               bool is_new_navigation) {
-  tracker_.OnCommitProvisionalLoad(GetFrameType(frame));
+  OnCommitLoad(IsMainFrame(frame));
 }
 
 void NetErrorHelper::DidFinishLoad(WebKit::WebFrame* frame) {
-  tracker_.OnFinishLoad(GetFrameType(frame));
+  OnFinishLoad(IsMainFrame(frame));
 }
 
-bool NetErrorHelper::OnMessageReceived(const IPC::Message& message) {
-  bool handled = true;
-
-  IPC_BEGIN_MESSAGE_MAP(NetErrorHelper, message)
-    IPC_MESSAGE_HANDLER(ChromeViewMsg_NetErrorInfo, OnNetErrorInfo)
-    IPC_MESSAGE_UNHANDLED(handled = false)
-  IPC_END_MESSAGE_MAP()
+void NetErrorHelper::OnStartLoad(bool is_main_frame, bool is_error_page) {
+  DVLOG(1) << "OnStartLoad(is_main_frame=" << is_main_frame
+           << ", is_error_page=" << is_error_page << ")";
+  if (!is_main_frame)
+    return;
 
-  return handled;
+  last_start_was_error_page_ = is_error_page;
 }
 
-void NetErrorHelper::OnNetErrorInfo(int dns_probe_result) {
-  DVLOG(1) << "Received DNS probe result " << dns_probe_result;
+void NetErrorHelper::OnFailLoad(bool is_main_frame, bool is_dns_error) {
+  DVLOG(1) << "OnFailLoad(is_main_frame=" << is_main_frame
+           << ", is_dns_error=" << is_dns_error << ")";
 
-  if (dns_probe_result < 0 ||
-      dns_probe_result >= chrome_common_net::DNS_PROBE_MAX) {
-    DLOG(WARNING) << "Ignoring DNS probe result: invalid result "
-                  << dns_probe_result;
-    NOTREACHED();
+  if (!is_main_frame)
     return;
+
+  last_fail_was_dns_error_ = is_dns_error;
+
+  if (is_dns_error) {
+    last_probe_status_ = chrome_common_net::DNS_PROBE_POSSIBLE;
+    // If the helper was forwarding probe results and another DNS error has
+    // occurred, stop forwarding probe results until the corresponding (new)
+    // error page loads.
+    forwarding_probe_results_ = false;
   }
+}
 
-  if (dns_error_page_state_ != NetErrorTracker::DNS_ERROR_PAGE_LOADED) {
-    DVLOG(1) << "Ignoring DNS probe result: not on DNS error page.";
+void NetErrorHelper::OnCommitLoad(bool is_main_frame) {
+  DVLOG(1) << "OnCommitLoad(is_main_frame=" << is_main_frame << ")";
+
+  if (!is_main_frame)
     return;
-  }
 
-  if (updated_error_page_) {
-    DVLOG(1) << "Ignoring DNS probe result: already updated error page.";
+  // Stop forwarding results.  If the page is a DNS error page, forwarding
+  // will resume once the page is loaded; if not, it should stay stopped until
+  // the next DNS error page.
+  forwarding_probe_results_ = false;
+}
+
+void NetErrorHelper::OnFinishLoad(bool is_main_frame) {
+  DVLOG(1) << "OnFinishLoad(is_main_frame=" << is_main_frame << ")";
+
+  if (!is_main_frame)
     return;
+
+  // If a DNS error page just finished loading, start forwarding probe results
+  // to it.
+  forwarding_probe_results_ =
+      last_fail_was_dns_error_ && last_start_was_error_page_;
+
+  if (forwarding_probe_results_ &&
+      last_probe_status_ != chrome_common_net::DNS_PROBE_POSSIBLE) {
+    DVLOG(1) << "Error page finished loading; sending saved status.";
+    UpdateErrorPage();
   }
+}
+
+bool NetErrorHelper::OnMessageReceived(const IPC::Message& message) {
+  bool handled = true;
 
-  UpdateErrorPage(static_cast<DnsProbeResult>(dns_probe_result));
-  updated_error_page_ = true;
+  IPC_BEGIN_MESSAGE_MAP(NetErrorHelper, message)
+    IPC_MESSAGE_HANDLER(ChromeViewMsg_NetErrorInfo, OnNetErrorInfo)
+    IPC_MESSAGE_UNHANDLED(handled = false)
+  IPC_END_MESSAGE_MAP()
+
+  return handled;
 }
 
-void NetErrorHelper::TrackerCallback(
-    NetErrorTracker::DnsErrorPageState state) {
-  dns_error_page_state_ = state;
+bool NetErrorHelper::GetErrorStringsForDnsProbe(
+    WebKit::WebFrame* frame,
+    const WebKit::WebURLError& error,
+    bool is_failed_post,
+    const std::string& locale,
+    base::DictionaryValue* error_strings) {
+  if (!IsMainFrame(frame))
+    return false;
 
-  if (state == NetErrorTracker::DNS_ERROR_PAGE_LOADED)
-    updated_error_page_ = false;
+  if (!IsDnsError(error))
+    return false;
+
+  // Get the strings for a fake "DNS probe possible" error.
+  WebKit::WebURLError fake_error;
+  fake_error.domain = WebKit::WebString::fromUTF8(
+      chrome_common_net::kDnsProbeErrorDomain);
+  fake_error.reason = chrome_common_net::DNS_PROBE_POSSIBLE;
+  fake_error.unreachableURL = error.unreachableURL;
+  LocalizedError::GetStrings(
+      fake_error, is_failed_post, locale, error_strings);
+  return true;
 }
 
-void NetErrorHelper::UpdateErrorPage(DnsProbeResult dns_probe_result) {
-  DVLOG(1) << "Updating error page with result " << dns_probe_result;
+void NetErrorHelper::OnNetErrorInfo(int status_num) {
+  DCHECK(status_num >= 0 && status_num < chrome_common_net::DNS_PROBE_MAX);
+
+  DVLOG(1) << "Received status " << DnsProbeStatusToString(status_num);
 
-  int net_error = DnsProbeResultToNetError(dns_probe_result);
-  if (net_error == net::OK)
+  DnsProbeStatus status = static_cast<DnsProbeStatus>(status_num);
+  DCHECK_NE(chrome_common_net::DNS_PROBE_POSSIBLE, status);
+
+  if (!(last_fail_was_dns_error_ || forwarding_probe_results_)) {
+    DVLOG(1) << "Ignoring NetErrorInfo: no DNS error";
     return;
+  }
+
+  last_probe_status_ = status;
 
-  DVLOG(1) << "net error code is " << net_error;
+  if (forwarding_probe_results_)
+    UpdateErrorPage();
+}
+
+void NetErrorHelper::UpdateErrorPage() {
+  DCHECK(forwarding_probe_results_);
 
   base::DictionaryValue error_strings;
-  LocalizedError::GetStrings(NetErrorToWebURLError(net_error),
+  LocalizedError::GetStrings(GetUpdatedError(),
                              is_failed_post_,
                              RenderThread::Get()->GetLocale(),
                              &error_strings);
 
-  // TODO(ttuttle): Update error page with error_strings.
+  std::string json;
+  JSONWriter::Write(&error_strings, &json);
+
+  std::string js = "if (window.updateForDnsProbe) "
+                   "updateForDnsProbe(" + json + ");";
+  string16 js16;
+  if (!UTF8ToUTF16(js.c_str(), js.length(), &js16)) {
+    NOTREACHED();
+    return;
+  }
+
+  DVLOG(1) << "Updating error page with status "
+           << chrome_common_net::DnsProbeStatusToString(last_probe_status_);
+  DVLOG(2) << "New strings: " << js;
+
+  string16 frame_xpath;
+  render_view()->EvaluateScript(frame_xpath, js16, 0, false);
+}
+
+WebKit::WebURLError NetErrorHelper::GetUpdatedError() const {
+  // If a probe didn't run or wasn't conclusive, restore the original error.
+  if (last_probe_status_ == chrome_common_net::DNS_PROBE_NOT_RUN ||
+      last_probe_status_ ==
+          chrome_common_net::DNS_PROBE_FINISHED_INCONCLUSIVE) {
+    return last_error_;
+  }
+
+  WebKit::WebURLError error;
+  error.domain = WebKit::WebString::fromUTF8(
+      chrome_common_net::kDnsProbeErrorDomain);
+  error.reason = last_probe_status_;
+  error.unreachableURL = last_error_.unreachableURL;
+
+  return error;
 }
diff --git a/chrome/renderer/net/net_error_helper.h b/chrome/renderer/net/net_error_helper.h
index cb33387e..84cdcb4 100644
--- a/chrome/renderer/net/net_error_helper.h
+++ b/chrome/renderer/net/net_error_helper.h
@@ -5,14 +5,23 @@
 #ifndef CHROME_RENDERER_NET_NET_ERROR_HELPER_H_
 #define CHROME_RENDERER_NET_NET_ERROR_HELPER_H_
 
+#include <string>
+
 #include "chrome/common/net/net_error_info.h"
-#include "chrome/common/net/net_error_tracker.h"
 #include "content/public/renderer/render_view_observer.h"
+#include "third_party/WebKit/public/platform/WebURLError.h"
+
+namespace base {
+class DictionaryValue;
+}
 
 namespace WebKit {
 class WebFrame;
 }
 
+// Listens for NetErrorInfo messages from the NetErrorTabHelper on the
+// browser side and updates the error page with more details (currently, just
+// DNS probe results) if/when available.
 class NetErrorHelper : public content::RenderViewObserver {
  public:
   explicit NetErrorHelper(content::RenderView* render_view);
@@ -31,14 +40,61 @@ class NetErrorHelper : public content::RenderViewObserver {
   // IPC::Listener implementation.
   virtual bool OnMessageReceived(const IPC::Message& message) OVERRIDE;
 
+  // Examines |frame| and |error| to see if this is an error worthy of a DNS
+  // probe.  If it is, initializes |error_strings| based on |error|,
+  // |is_failed_post|, and |locale| with suitable strings and returns true.
+  // If not, returns false, in which case the caller should look up error
+  // strings directly using LocalizedError::GetNavigationErrorStrings.
+  static bool GetErrorStringsForDnsProbe(
+      WebKit::WebFrame* frame,
+      const WebKit::WebURLError& error,
+      bool is_failed_post,
+      const std::string& locale,
+      base::DictionaryValue* error_strings);
+
+ protected:
+  // These methods handle tracking the actual state of the page; this allows
+  // unit-testing of the state tracking without having to mock out WebFrames
+  // and such.
+  void OnStartLoad(bool is_main_frame, bool is_error_page);
+  void OnFailLoad(bool is_main_frame, bool is_dns_error);
+  void OnCommitLoad(bool is_main_frame);
+  void OnFinishLoad(bool is_main_frame);
+
+  void OnNetErrorInfo(int status);
+
+  // |UpdateErrorPage| is virtual so it can be mocked out in the unittest.
+  virtual void UpdateErrorPage();
+
+  // The last DnsProbeStatus received from the browser.
+  chrome_common_net::DnsProbeStatus last_probe_status_;
+
  private:
-  void OnNetErrorInfo(int dns_probe_result);
-  void TrackerCallback(NetErrorTracker::DnsErrorPageState state);
-  void UpdateErrorPage(chrome_common_net::DnsProbeResult dns_probe_result);
+  WebKit::WebURLError GetUpdatedError() const;
+
+  // Whether the last provisional load started was for an error page.
+  bool last_start_was_error_page_;
+
+  // Whether the last provisional load failure failed with a DNS error.
+  bool last_fail_was_dns_error_;
+
+  // Ideally, this would be simply "last_commit_was_dns_error_page_".
+  //
+  // Unfortunately, that breaks if two DNS errors occur in a row; after the
+  // second failure, but before the second page commits, the helper can receive
+  // probe results.  If all it knows is that the last commit was a DNS error
+  // page, it will cheerfully forward the results for the second probe to the
+  // first page.
+  //
+  // Thus, the semantics of this flag are a little weird.  It is set whenever
+  // a DNS error page commits, and cleared whenever any other page commits,
+  // but it is also cleared whenever a DNS error occurs, to prevent the race
+  // described above.
+  bool forwarding_probe_results_;
+
+  // The last main frame error seen by the helper.
+  WebKit::WebURLError last_error_;
 
-  NetErrorTracker tracker_;
-  NetErrorTracker::DnsErrorPageState dns_error_page_state_;
-  bool updated_error_page_;
   bool is_failed_post_;
 };
 
diff --git a/chrome/renderer/net/net_error_helper_unittest.cc b/chrome/renderer/net/net_error_helper_unittest.cc
new file mode 100644
index 0000000..828c34e
--- /dev/null
+++ b/chrome/renderer/net/net_error_helper_unittest.cc
@@ -0,0 +1,412 @@
+// Copyright 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "chrome/renderer/net/net_error_helper.h"
+
+#include "base/logging.h"
+#include "chrome/common/net/net_error_info.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+using chrome_common_net::DnsProbeStatus;
+using chrome_common_net::DnsProbeStatusToString;
+
+// NetErrorHelperTest cases consist of a string of these steps.
+enum TestStep {
+  // Simulate a provisional load start, fail, commit or a finish-load event.
+  // (Start and fail differentiate between normal and error pages.)
+  LOAD_NORMAL_START, LOAD_NORMAL_FAIL, LOAD_ERROR_START,
+  LOAD_COMMIT, LOAD_FINISH,
+
+  // Simulate an IPC from the browser with DNS_PROBE_STARTED, _NOT_RUN, or
+  // _FINISHED_NXDOMAIN.
+  STATUS_STARTED, STATUS_NOT_RUN, STATUS_FINISHED,
+
+  // Expect that the *next* step will cause an update.  (Any step that is not
+  // prefixed by this pseudo-step is expected *not* to cause an update.)
+  EXPECT_UPDATE
+};
+
+class TestNetErrorHelper : public NetErrorHelper {
+ public:
+  TestNetErrorHelper()
+      : NetErrorHelper(NULL),
+        mock_page_update_count_(0),
+        mock_displayed_probe_status_(chrome_common_net::DNS_PROBE_MAX) {}
+
+  virtual ~TestNetErrorHelper() {}
+
+  void StartLoad(bool is_main_frame, bool is_error_page) {
+    OnStartLoad(is_main_frame, is_error_page);
+  }
+
+  void FailLoad(bool is_main_frame, bool is_dns_error) {
+    OnFailLoad(is_main_frame, is_dns_error);
+  }
+
+  void CommitLoad(bool is_main_frame) {
+    OnCommitLoad(is_main_frame);
+  }
+
+  void FinishLoad(bool is_main_frame) {
+    OnFinishLoad(is_main_frame);
+  }
+
+  void ReceiveProbeStatus(DnsProbeStatus status) {
+    OnNetErrorInfo(static_cast<int>(status));
+  }
+
+  int mock_page_update_count() const { return mock_page_update_count_;  }
+  DnsProbeStatus mock_displayed_probe_status() const {
+    return mock_displayed_probe_status_;
+  }
+
+ protected:
+  virtual void UpdateErrorPage() OVERRIDE {
+    DVLOG(1) << "Updating error page with status "
+             << DnsProbeStatusToString(last_probe_status_);
+    mock_page_update_count_++;
+    mock_displayed_probe_status_ = last_probe_status_;
+  }
+
+ private:
+  int mock_page_update_count_;
+  DnsProbeStatus mock_displayed_probe_status_;
+};
+
+class NetErrorHelperTest : public testing::Test {
+ protected:
+  enum MainFrame { SUB_FRAME, MAIN_FRAME };
+  enum ErrorPage { NORMAL_PAGE, ERROR_PAGE };
+  enum ErrorType { OTHER_ERROR, DNS_ERROR };
+
+  void StartLoad(MainFrame main_frame, ErrorPage error_page) {
+    helper_.StartLoad(main_frame == MAIN_FRAME, error_page == ERROR_PAGE);
+  }
+
+  void FailLoad(MainFrame main_frame, ErrorType error_type) {
+    helper_.FailLoad(main_frame == MAIN_FRAME, error_type == DNS_ERROR);
+  }
+
+  void CommitLoad(MainFrame main_frame) {
+    helper_.CommitLoad(main_frame == MAIN_FRAME);
+  }
+
+  void FinishLoad(MainFrame main_frame) {
+    helper_.FinishLoad(main_frame == MAIN_FRAME);
+  }
+
+  void ReceiveProbeStatus(DnsProbeStatus status) {
+    helper_.ReceiveProbeStatus(status);
+  }
+
+  void RunTest(const TestStep steps[], int step_count);
+
+  int page_update_count() const { return helper_.mock_page_update_count(); }
+  DnsProbeStatus displayed_probe_status() const {
+    return helper_.mock_displayed_probe_status();
+  }
+
+ private:
+  TestNetErrorHelper helper_;
+};
+
+void NetErrorHelperTest::RunTest(const TestStep steps[], int step_count) {
+  // Whether the next instruction is expected to cause an update (since the
+  // step right before it was EXPECT_UPDATE) or not.
+  bool update_expected = false;
+  int expected_update_count = page_update_count();
+  // The last status that the test simulated receiving from the browser.
+  // When an update is expected, the status is expected to match this.
+  chrome_common_net::DnsProbeStatus last_status_received =
+      chrome_common_net::DNS_PROBE_POSSIBLE;
+
+  for (int i = 0; i < step_count; i++) {
+    switch (steps[i]) {
+    case LOAD_NORMAL_START:
+      StartLoad(MAIN_FRAME, NORMAL_PAGE);
+      break;
+    case LOAD_NORMAL_FAIL:
+      FailLoad(MAIN_FRAME, DNS_ERROR);
+      break;
+    case LOAD_ERROR_START:
+      StartLoad(MAIN_FRAME, ERROR_PAGE);
+      break;
+    case LOAD_COMMIT:
+      CommitLoad(MAIN_FRAME);
+      break;
+    case LOAD_FINISH:
+      FinishLoad(MAIN_FRAME);
+      break;
+    case STATUS_STARTED:
+      ReceiveProbeStatus(chrome_common_net::DNS_PROBE_STARTED);
+      last_status_received = chrome_common_net::DNS_PROBE_STARTED;
+      break;
+    case STATUS_NOT_RUN:
+      ReceiveProbeStatus(chrome_common_net::DNS_PROBE_NOT_RUN);
+      last_status_received = chrome_common_net::DNS_PROBE_NOT_RUN;
+      break;
+    case STATUS_FINISHED:
+      ReceiveProbeStatus(chrome_common_net::DNS_PROBE_FINISHED_NXDOMAIN);
+      last_status_received = chrome_common_net::DNS_PROBE_FINISHED_NXDOMAIN;
+      break;
+    case EXPECT_UPDATE:
+      ASSERT_FALSE(update_expected);
+      update_expected = true;
+      // Skip to next step to see if it updates the status, instead of
+      // checking whether EXPECT_UPDATE itself caused an update.
+      continue;
+    }
+
+    if (update_expected) {
+      DCHECK_NE(chrome_common_net::DNS_PROBE_POSSIBLE, last_status_received);
+      ++expected_update_count;
+
+      EXPECT_EQ(last_status_received, displayed_probe_status());
+      if (displayed_probe_status() != last_status_received) {
+        LOG(ERROR) << "Unexpected status at step " << i << ".";
+        return;
+      }
+    }
+
+    EXPECT_EQ(expected_update_count, page_update_count());
+    if (page_update_count() != expected_update_count) {
+      LOG(ERROR) << (update_expected ? "Missing" : "Spurious")
+                 << " update at step " << i << ".";
+      return;
+    }
+
+    update_expected = false;
+  }
+
+  DCHECK(!update_expected);
+}
+
+TEST_F(NetErrorHelperTest, Null) {
+  // Test that we can simply create and destroy a NetErrorHelper.
+}
+
+TEST_F(NetErrorHelperTest, SuccessfulPageLoad) {
+  StartLoad(MAIN_FRAME, NORMAL_PAGE);
+  CommitLoad(MAIN_FRAME);
+  FinishLoad(MAIN_FRAME);
+
+  // Ignore spurious status.
+  ReceiveProbeStatus(chrome_common_net::DNS_PROBE_FINISHED_NXDOMAIN);
+  EXPECT_EQ(0, page_update_count());
+}
+
+TEST_F(NetErrorHelperTest, MainFrameNonDnsError) {
+  StartLoad(MAIN_FRAME, NORMAL_PAGE);
+  FailLoad(MAIN_FRAME, OTHER_ERROR);
+  StartLoad(MAIN_FRAME, ERROR_PAGE);
+  CommitLoad(MAIN_FRAME);
+  FinishLoad(MAIN_FRAME);
+
+  // Ignore spurious status.
+  ReceiveProbeStatus(chrome_common_net::DNS_PROBE_FINISHED_NXDOMAIN);
+  EXPECT_EQ(0, page_update_count());
+}
+
+TEST_F(NetErrorHelperTest, SubFrameDnsError) {
+  StartLoad(SUB_FRAME, NORMAL_PAGE);
+  FailLoad(SUB_FRAME, DNS_ERROR);
+  StartLoad(SUB_FRAME, ERROR_PAGE);
+  CommitLoad(SUB_FRAME);
+  FinishLoad(SUB_FRAME);
+
+  // Ignore spurious status.
+  ReceiveProbeStatus(chrome_common_net::DNS_PROBE_FINISHED_NXDOMAIN);
+  EXPECT_EQ(0, page_update_count());
+}
+
+TEST_F(NetErrorHelperTest, FinishedAfterFail) {
+  const TestStep steps[] = {
+    LOAD_NORMAL_START, LOAD_NORMAL_FAIL, STATUS_FINISHED, LOAD_ERROR_START,
+    LOAD_COMMIT, EXPECT_UPDATE, LOAD_FINISH
+  };
+  RunTest(steps, arraysize(steps));
+}
+
+TEST_F(NetErrorHelperTest, FinishedAfterFail_StartedAfterFail) {
+  const TestStep steps[] = {
+    LOAD_NORMAL_START, LOAD_NORMAL_FAIL, STATUS_STARTED, STATUS_FINISHED,
+    LOAD_ERROR_START, LOAD_COMMIT, EXPECT_UPDATE, LOAD_FINISH
+  };
+  RunTest(steps, arraysize(steps));
+}
+
+TEST_F(NetErrorHelperTest, FinishedAfterStart) {
+  const TestStep steps[] = {
+    LOAD_NORMAL_START, LOAD_NORMAL_FAIL, LOAD_ERROR_START, STATUS_FINISHED,
+    LOAD_COMMIT, EXPECT_UPDATE, LOAD_FINISH
+  };
+  RunTest(steps, arraysize(steps));
+}
+
+TEST_F(NetErrorHelperTest, FinishedAfterStart_StartedAfterFail) {
+  const TestStep steps[] = {
+    LOAD_NORMAL_START, LOAD_NORMAL_FAIL, STATUS_STARTED, LOAD_ERROR_START,
+    STATUS_FINISHED, LOAD_COMMIT, EXPECT_UPDATE, LOAD_FINISH
+  };
+  RunTest(steps, arraysize(steps));
+}
+
+TEST_F(NetErrorHelperTest, FinishedAfterStart_StartedAfterStart) {
+  const TestStep steps[] = {
+    LOAD_NORMAL_START, LOAD_NORMAL_FAIL, STATUS_STARTED, LOAD_ERROR_START,
+    STATUS_FINISHED, LOAD_COMMIT, EXPECT_UPDATE, LOAD_FINISH
+  };
+  RunTest(steps, arraysize(steps));
+}
+
+TEST_F(NetErrorHelperTest, FinishedAfterCommit) {
+  const TestStep steps[] = {
+    LOAD_NORMAL_START, LOAD_NORMAL_FAIL, LOAD_ERROR_START, LOAD_COMMIT,
+    STATUS_FINISHED, EXPECT_UPDATE, LOAD_FINISH
+  };
+  RunTest(steps, arraysize(steps));
+}
+
+TEST_F(NetErrorHelperTest, FinishedAfterCommit_StartedAfterFail) {
+  const TestStep steps[] = {
+    LOAD_NORMAL_START, LOAD_NORMAL_FAIL, STATUS_STARTED, LOAD_ERROR_START,
+    LOAD_COMMIT, STATUS_FINISHED, EXPECT_UPDATE, LOAD_FINISH
+  };
+  RunTest(steps, arraysize(steps));
+}
+
+TEST_F(NetErrorHelperTest, FinishedAfterCommit_StartedAfterStart) {
+  const TestStep steps[] = {
+    LOAD_NORMAL_START, LOAD_NORMAL_FAIL, LOAD_ERROR_START, STATUS_STARTED,
+    LOAD_ERROR_START, LOAD_COMMIT, STATUS_FINISHED, EXPECT_UPDATE, LOAD_FINISH
+  };
+  RunTest(steps, arraysize(steps));
+}
+
+TEST_F(NetErrorHelperTest, FinishedAfterCommit_StartedAfterCommit) {
+  const TestStep steps[] = {
+    LOAD_NORMAL_START, LOAD_NORMAL_FAIL, LOAD_ERROR_START, LOAD_COMMIT,
+    STATUS_STARTED, STATUS_FINISHED, EXPECT_UPDATE, LOAD_FINISH
+  };
+  RunTest(steps, arraysize(steps));
+}
+
+TEST_F(NetErrorHelperTest, FinishedAfterFinish) {
+  const TestStep steps[] = {
+    LOAD_NORMAL_START, LOAD_NORMAL_FAIL, LOAD_ERROR_START, LOAD_COMMIT,
+    LOAD_FINISH, EXPECT_UPDATE, STATUS_FINISHED
+  };
+  RunTest(steps, arraysize(steps));
+}
+
+TEST_F(NetErrorHelperTest, FinishedAfterFinish_StartAfterFail) {
+  const TestStep steps[] = {
+    LOAD_NORMAL_START, LOAD_NORMAL_FAIL, STATUS_STARTED, LOAD_ERROR_START,
+    LOAD_COMMIT, EXPECT_UPDATE, LOAD_FINISH, EXPECT_UPDATE, STATUS_FINISHED
+  };
+  RunTest(steps, arraysize(steps));
+}
+
+TEST_F(NetErrorHelperTest, FinishedAfterFinish_StartAfterStart) {
+  const TestStep steps[] = {
+    LOAD_NORMAL_START, LOAD_NORMAL_FAIL, LOAD_ERROR_START, STATUS_STARTED,
+    LOAD_COMMIT, EXPECT_UPDATE, LOAD_FINISH, EXPECT_UPDATE, STATUS_FINISHED
+  };
+  RunTest(steps, arraysize(steps));
+}
+
+TEST_F(NetErrorHelperTest, FinishedAfterFinish_StartAfterCommit) {
+  const TestStep steps[] = {
+    LOAD_NORMAL_START, LOAD_NORMAL_FAIL, LOAD_ERROR_START, LOAD_COMMIT,
+    STATUS_STARTED, EXPECT_UPDATE, LOAD_FINISH, EXPECT_UPDATE, STATUS_FINISHED
+  };
+  RunTest(steps, arraysize(steps));
+}
+
+TEST_F(NetErrorHelperTest, FinishedAfterFinish_StartAfterFinish) {
+  const TestStep steps[] = {
+    LOAD_NORMAL_START, LOAD_NORMAL_FAIL, LOAD_ERROR_START, LOAD_COMMIT,
+    LOAD_FINISH, EXPECT_UPDATE, STATUS_STARTED, EXPECT_UPDATE, STATUS_FINISHED
+  };
+  RunTest(steps, arraysize(steps));
+}
+
+TEST_F(NetErrorHelperTest, FinishedAfterNewStart) {
+  const TestStep steps[] = {
+    LOAD_NORMAL_START, LOAD_NORMAL_FAIL, LOAD_ERROR_START, LOAD_COMMIT,
+    LOAD_FINISH, LOAD_NORMAL_START, EXPECT_UPDATE, STATUS_FINISHED,
+    LOAD_COMMIT, LOAD_FINISH
+  };
+  RunTest(steps, arraysize(steps));
+}
+
+TEST_F(NetErrorHelperTest, NotRunAfterFail) {
+  const TestStep steps[] = {
+    LOAD_NORMAL_START, LOAD_NORMAL_FAIL, STATUS_NOT_RUN, LOAD_ERROR_START,
+    LOAD_COMMIT, EXPECT_UPDATE, LOAD_FINISH
+  };
+  RunTest(steps, arraysize(steps));
+}
+
+TEST_F(NetErrorHelperTest, NotRunAfterStart) {
+  const TestStep steps[] = {
+    LOAD_NORMAL_START, LOAD_NORMAL_FAIL, LOAD_ERROR_START, STATUS_NOT_RUN,
+    LOAD_COMMIT, EXPECT_UPDATE, LOAD_FINISH
+  };
+  RunTest(steps, arraysize(steps));
+}
+
+TEST_F(NetErrorHelperTest, NotRunAfterCommit) {
+  const TestStep steps[] = {
+    LOAD_NORMAL_START, LOAD_NORMAL_FAIL, LOAD_ERROR_START, LOAD_COMMIT,
+    STATUS_NOT_RUN, EXPECT_UPDATE, LOAD_FINISH
+  };
+  RunTest(steps, arraysize(steps));
+}
+
+TEST_F(NetErrorHelperTest, NotRunAfterFinish) {
+  const TestStep steps[] = {
+    LOAD_NORMAL_START, LOAD_NORMAL_FAIL, LOAD_ERROR_START, LOAD_COMMIT,
+    LOAD_FINISH, EXPECT_UPDATE, STATUS_NOT_RUN
+  };
+  RunTest(steps, arraysize(steps));
+}
+
+TEST_F(NetErrorHelperTest, FinishedAfterNewCommit) {
+  const TestStep steps[] = {
+    LOAD_NORMAL_START, LOAD_NORMAL_FAIL, LOAD_ERROR_START, LOAD_COMMIT,
+    LOAD_FINISH, LOAD_NORMAL_START, LOAD_COMMIT, STATUS_FINISHED, LOAD_FINISH
+  };
+  RunTest(steps, arraysize(steps));
+}
+
+TEST_F(NetErrorHelperTest, FinishedAfterNewFinish) {
+  const TestStep steps[] = {
+    LOAD_NORMAL_START, LOAD_NORMAL_FAIL, LOAD_ERROR_START, LOAD_COMMIT,
+    LOAD_FINISH, LOAD_NORMAL_START, LOAD_COMMIT, LOAD_FINISH, STATUS_FINISHED
+  };
+  RunTest(steps, arraysize(steps));
+}
+
+// Two iterations of FinishedAfterStart_StartAfterFail
+TEST_F(NetErrorHelperTest, TwoProbes_FinishedAfterStart_StartAfterFail) {
+  const TestStep steps[] = {
+    LOAD_NORMAL_START, LOAD_NORMAL_FAIL, STATUS_STARTED, LOAD_ERROR_START,
+    STATUS_FINISHED, LOAD_COMMIT, EXPECT_UPDATE, LOAD_FINISH,
+    LOAD_NORMAL_START, LOAD_NORMAL_FAIL, STATUS_STARTED, LOAD_ERROR_START,
+    STATUS_FINISHED, LOAD_COMMIT, EXPECT_UPDATE, LOAD_FINISH
+  };
+  RunTest(steps, arraysize(steps));
+}
+
+// Two iterations of FinishedAfterFinish
+TEST_F(NetErrorHelperTest, TwoProbes_FinishedAfterFinish) {
+  const TestStep steps[] = {
+    LOAD_NORMAL_START, LOAD_NORMAL_FAIL, LOAD_ERROR_START, LOAD_COMMIT,
+    LOAD_FINISH, EXPECT_UPDATE, STATUS_FINISHED,
+    LOAD_NORMAL_START, LOAD_NORMAL_FAIL, LOAD_ERROR_START, LOAD_COMMIT,
+    LOAD_FINISH, EXPECT_UPDATE, STATUS_FINISHED
+  };
+  RunTest(steps, arraysize(steps));
+}
diff --git a/chrome/renderer/resources/neterror.html b/chrome/renderer/resources/neterror.html
index bb301f2..41c80c8 100644
--- a/chrome/renderer/resources/neterror.html
+++ b/chrome/renderer/resources/neterror.html
@@ -307,6 +307,12 @@ function toggleHelpBox() {
 if (window.top.location != window.location)
   document.documentElement.setAttribute('subframe', '');
 
+function updateForDnsProbe(strings) {
+  var context = new JsEvalContext(strings);
+  jstProcess(context, document.getElementById('help-box-outer'));
+  jstProcess(context, document.getElementById('details'));
+}
+
 </script>
 
 <body id="t">