Implement blocking for webRequest.onBeforeRequest extension event.

I did some measurements with a Release build of chrome, both manually and via the page cycler tests. It seems that a simple empty blocking event listener can add anywhere from a 1 to 30ms delay to request times, largely depending on how many requests are in the queue (when many requests come at once, the last ones to be processed by the extension are delayed the longest).

From page cycler data (on my local machine), the average increase in page load time seems to be around 6ms. This is independent of total page load time (which makes sense).

BUG=60101
TEST=covered by apitests

Review URL: http://codereview.chromium.org/6574049

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@77339 0039d316-1c4b-4281-b951-d872f2087c98

39 files changed, 631 insertions, 377 deletions

diff --git a/chrome/browser/extensions/extension_event_router.cc b/chrome/browser/extensions/extension_event_router.cc
index 1b170e0..fc8bd87 100644
--- a/chrome/browser/extensions/extension_event_router.cc
+++ b/chrome/browser/extensions/extension_event_router.cc
@@ -34,6 +34,14 @@ static void DispatchEvent(RenderProcessHost* renderer,
       extension_id, kDispatchEvent, args, event_url));
 }
 
+static void NotifyEventListenerRemovedOnIOThread(
+    ProfileId profile_id,
+    const std::string& extension_id,
+    const std::string& sub_event_name) {
+  ExtensionWebRequestEventRouter::GetInstance()->RemoveEventListener(
+      profile_id, extension_id, sub_event_name);
+}
+
 }  // namespace
 
 struct ExtensionEventRouter::EventListener {
@@ -120,8 +128,11 @@ void ExtensionEventRouter::RemoveEventListener(
   if (event_name.compare(extension_processes_api_constants::kOnUpdated) == 0)
     ExtensionProcessesEventRouter::GetInstance()->ListenerRemoved();
 
-  ExtensionWebRequestEventRouter::RemoveEventListenerOnUIThread(
-      listener.extension_id, event_name);
+  BrowserThread::PostTask(
+      BrowserThread::IO, FROM_HERE,
+      NewRunnableFunction(
+          &NotifyEventListenerRemovedOnIOThread,
+          profile_->GetRuntimeId(), listener.extension_id, event_name));
 }
 
 bool ExtensionEventRouter::HasEventListener(const std::string& event_name) {
diff --git a/chrome/browser/extensions/extension_function_dispatcher.cc b/chrome/browser/extensions/extension_function_dispatcher.cc
index 11abc26..4fb7af3 100644
--- a/chrome/browser/extensions/extension_function_dispatcher.cc
+++ b/chrome/browser/extensions/extension_function_dispatcher.cc
@@ -298,6 +298,7 @@ void FactoryRegistry::ResetFunctions() {
 
   // WebRequest.
   RegisterFunction<WebRequestAddEventListener>();
+  RegisterFunction<WebRequestEventHandled>();
 
   // Preferences.
   RegisterFunction<GetPreferenceFunction>();
diff --git a/chrome/browser/extensions/extension_info_map.cc b/chrome/browser/extensions/extension_info_map.cc
index 254e7ec..e7a4b09 100644
--- a/chrome/browser/extensions/extension_info_map.cc
+++ b/chrome/browser/extensions/extension_info_map.cc
@@ -25,10 +25,6 @@ ExtensionInfoMap::~ExtensionInfoMap() {
 void ExtensionInfoMap::AddExtension(const Extension* extension) {
   CheckOnValidThread();
   extension_info_[extension->id()] = extension;
-
-  // Our map has already added a reference. Balance the reference given at the
-  // call-site.
-  extension->Release();
 }
 
 void ExtensionInfoMap::RemoveExtension(const std::string& id) {
diff --git a/chrome/browser/extensions/extension_info_map_unittest.cc b/chrome/browser/extensions/extension_info_map_unittest.cc
index 7d82dd2..dd814d1 100644
--- a/chrome/browser/extensions/extension_info_map_unittest.cc
+++ b/chrome/browser/extensions/extension_info_map_unittest.cc
@@ -83,14 +83,9 @@ TEST_F(ExtensionInfoMapTest, RefCounting) {
   EXPECT_TRUE(extension2->HasOneRef());
   EXPECT_TRUE(extension3->HasOneRef());
 
-  // Add a ref to each extension and give it to the info map. The info map
-  // expects the caller to add a ref for it, but then assumes ownership of that
-  // reference.
-  extension1->AddRef();
+  // Add a ref to each extension and give it to the info map.
   info_map->AddExtension(extension1);
-  extension2->AddRef();
   info_map->AddExtension(extension2);
-  extension3->AddRef();
   info_map->AddExtension(extension3);
 
   // Release extension1, and the info map should have the only ref.
@@ -114,9 +109,7 @@ TEST_F(ExtensionInfoMapTest, Properties) {
   scoped_refptr<Extension> extension1(CreateExtension("extension1"));
   scoped_refptr<Extension> extension2(CreateExtension("extension2"));
 
-  extension1->AddRef();
   info_map->AddExtension(extension1);
-  extension2->AddRef();
   info_map->AddExtension(extension2);
 
   EXPECT_EQ(extension1->name(),
@@ -143,9 +136,7 @@ TEST_F(ExtensionInfoMapTest, CheckPermissions) {
   ASSERT_TRUE(app->is_app());
   ASSERT_TRUE(app->web_extent().ContainsURL(app_url));
 
-  app->AddRef();
   info_map->AddExtension(app);
-  extension->AddRef();
   info_map->AddExtension(extension);
 
   // The app should have the notifications permission, either from a
diff --git a/chrome/browser/extensions/extension_webnavigation_api.cc b/chrome/browser/extensions/extension_webnavigation_api.cc
index 86c4579..5a52612 100644
--- a/chrome/browser/extensions/extension_webnavigation_api.cc
+++ b/chrome/browser/extensions/extension_webnavigation_api.cc
@@ -7,6 +7,7 @@
 #include "chrome/browser/extensions/extension_webnavigation_api.h"
 
 #include "base/json/json_writer.h"
+#include "base/string_number_conversions.h"
 #include "base/time.h"
 #include "base/values.h"
 #include "chrome/browser/extensions/extension_event_router.h"
@@ -64,7 +65,8 @@ void DispatchOnBeforeNavigate(NavigationController* controller,
                    ExtensionTabUtil::GetTabId(controller->tab_contents()));
   dict->SetString(keys::kUrlKey, details->url().spec());
   dict->SetInteger(keys::kFrameIdKey, GetFrameId(details));
-  dict->SetInteger(keys::kRequestIdKey, static_cast<int>(request_id));
+  dict->SetString(keys::kRequestIdKey,
+                  base::Uint64ToString(request_id));
   dict->SetDouble(keys::kTimeStampKey, MilliSecondsFromTime(base::Time::Now()));
   args.Append(dict);
 
diff --git a/chrome/browser/extensions/extension_webrequest_api.cc b/chrome/browser/extensions/extension_webrequest_api.cc
index a68f2b3..46d14c1 100644
--- a/chrome/browser/extensions/extension_webrequest_api.cc
+++ b/chrome/browser/extensions/extension_webrequest_api.cc
@@ -7,13 +7,18 @@
 #include <algorithm>
 
 #include "base/json/json_writer.h"
+#include "base/metrics/histogram.h"
+#include "base/string_number_conversions.h"
 #include "base/values.h"
 #include "chrome/browser/extensions/extension_event_router_forwarder.h"
 #include "chrome/browser/extensions/extension_webrequest_api_constants.h"
+#include "chrome/browser/profiles/profile.h"
 #include "chrome/common/extensions/extension.h"
 #include "chrome/common/extensions/extension_extent.h"
 #include "chrome/common/extensions/url_pattern.h"
 #include "content/browser/browser_thread.h"
+#include "net/base/net_errors.h"
+#include "net/url_request/url_request.h"
 #include "googleurl/src/gurl.h"
 
 namespace keys = extension_webrequest_api_constants;
@@ -56,19 +61,26 @@ static bool IsValidRequestFilterType(const std::string& type) {
 }
 
 static void AddEventListenerOnIOThread(
+    ProfileId profile_id,
     const std::string& extension_id,
     const std::string& event_name,
     const std::string& sub_event_name,
     const ExtensionWebRequestEventRouter::RequestFilter& filter,
     int extra_info_spec) {
   ExtensionWebRequestEventRouter::GetInstance()->AddEventListener(
-      extension_id, event_name, sub_event_name, filter, extra_info_spec);
+      profile_id, extension_id, event_name, sub_event_name, filter,
+      extra_info_spec);
 }
 
-static void RemoveEventListenerOnIOThread(
-    const std::string& extension_id, const std::string& sub_event_name) {
-  ExtensionWebRequestEventRouter::GetInstance()->RemoveEventListener(
-      extension_id, sub_event_name);
+static void EventHandledOnIOThread(
+    ProfileId profile_id,
+    const std::string& extension_id,
+    const std::string& event_name,
+    const std::string& sub_event_name,
+    uint64 request_id,
+    bool cancel) {
+  ExtensionWebRequestEventRouter::GetInstance()->OnEventHandled(
+      profile_id, extension_id, event_name, sub_event_name, request_id, cancel);
 }
 
 }  // namespace
@@ -94,6 +106,7 @@ struct ExtensionWebRequestEventRouter::ExtraInfoSpec {
     RESPONSE_HEADERS = 1<<3,
     REDIRECT_REQUEST_LINE = 1<<4,
     REDIRECT_REQUEST_HEADERS = 1<<5,
+    BLOCKING = 1<<5,
   };
 
   static bool InitFromValue(const ListValue& value, int* extra_info_spec);
@@ -107,6 +120,7 @@ struct ExtensionWebRequestEventRouter::EventListener {
   std::string sub_event_name;
   RequestFilter filter;
   int extra_info_spec;
+  mutable std::set<uint64> blocked_requests;
 
   // Comparator to work with std::set.
   bool operator<(const EventListener& that) const {
@@ -119,6 +133,21 @@ struct ExtensionWebRequestEventRouter::EventListener {
   }
 };
 
+// Contains info about requests that are blocked waiting for a response from
+// an extension.
+struct ExtensionWebRequestEventRouter::BlockedRequest {
+  // The number of event handlers that we are awaiting a response from.
+  int num_handlers_blocking;
+
+  // The callback to call when we get a response from all event handlers.
+  net::CompletionCallback* callback;
+
+  // Time the request was issued. Used for logging purposes.
+  base::Time request_time;
+
+  BlockedRequest() : num_handlers_blocking(0), callback(NULL) {}
+};
+
 bool ExtensionWebRequestEventRouter::RequestFilter::InitFromValue(
     const DictionaryValue& value) {
   for (DictionaryValue::key_iterator key = value.begin_keys();
@@ -182,6 +211,8 @@ bool ExtensionWebRequestEventRouter::ExtraInfoSpec::InitFromValue(
       *extra_info_spec |= REDIRECT_REQUEST_LINE;
     else if (str == "redirectRequestHeaders")
       *extra_info_spec |= REDIRECT_REQUEST_HEADERS;
+    else if (str == "blocking")
+      *extra_info_spec |= BLOCKING;
     else
       return false;
   }
@@ -199,36 +230,27 @@ ExtensionWebRequestEventRouter::ExtensionWebRequestEventRouter() {
 ExtensionWebRequestEventRouter::~ExtensionWebRequestEventRouter() {
 }
 
-// static
-void ExtensionWebRequestEventRouter::RemoveEventListenerOnUIThread(
-    const std::string& extension_id, const std::string& sub_event_name) {
-  BrowserThread::PostTask(
-      BrowserThread::IO, FROM_HERE,
-      NewRunnableFunction(
-          &RemoveEventListenerOnIOThread,
-          extension_id, sub_event_name));
-}
-
-void ExtensionWebRequestEventRouter::OnBeforeRequest(
-    ExtensionEventRouterForwarder* event_router,
+bool ExtensionWebRequestEventRouter::OnBeforeRequest(
     ProfileId profile_id,
-    const GURL& url,
-    const std::string& method) {
+    ExtensionEventRouterForwarder* event_router,
+    net::URLRequest* request,
+    net::CompletionCallback* callback) {
   // TODO(jochen): Figure out what to do with events from the system context.
   if (profile_id == Profile::kInvalidProfileId)
-    return;
+    return false;
   std::vector<const EventListener*> listeners =
-      GetMatchingListeners(keys::kOnBeforeRequest, url);
+      GetMatchingListeners(profile_id, keys::kOnBeforeRequest, request->url());
   if (listeners.empty())
-    return;
+    return false;
 
   ListValue args;
   DictionaryValue* dict = new DictionaryValue();
-  dict->SetString(keys::kUrlKey, url.spec());
-  dict->SetString(keys::kMethodKey, method);
+  dict->SetString(keys::kUrlKey, request->url().spec());
+  dict->SetString(keys::kMethodKey, request->method());
   // TODO(mpcomplete): implement
   dict->SetInteger(keys::kTabIdKey, 0);
-  dict->SetInteger(keys::kRequestIdKey, 0);
+  dict->SetString(keys::kRequestIdKey,
+                  base::Uint64ToString(request->identifier()));
   dict->SetString(keys::kTypeKey, "main_frame");
   dict->SetInteger(keys::kTimeStampKey, 1);
   args.Append(dict);
@@ -236,16 +258,58 @@ void ExtensionWebRequestEventRouter::OnBeforeRequest(
   std::string json_args;
   base::JSONWriter::Write(&args, false, &json_args);
 
+  // TODO(mpcomplete): Consider consolidating common (extension_id,json_args)
+  // pairs into a single message sent to a list of sub_event_names.
+  int num_handlers_blocking = 0;
   for (std::vector<const EventListener*>::iterator it = listeners.begin();
        it != listeners.end(); ++it) {
-
     event_router->DispatchEventToExtension(
         (*it)->extension_id, (*it)->sub_event_name, json_args,
         profile_id, true, GURL());
+    if ((*it)->extra_info_spec & ExtraInfoSpec::BLOCKING) {
+      (*it)->blocked_requests.insert(request->identifier());
+      ++num_handlers_blocking;
+    }
+  }
+
+  if (num_handlers_blocking > 0) {
+    CHECK(blocked_requests_.find(request->identifier()) ==
+          blocked_requests_.end());
+    blocked_requests_[request->identifier()].num_handlers_blocking =
+        num_handlers_blocking;
+    blocked_requests_[request->identifier()].callback = callback;
+    blocked_requests_[request->identifier()].request_time =
+        request->request_time();
+
+    return true;
   }
+
+  return false;
+}
+
+void ExtensionWebRequestEventRouter::OnEventHandled(
+    ProfileId profile_id,
+    const std::string& extension_id,
+    const std::string& event_name,
+    const std::string& sub_event_name,
+    uint64 request_id,
+    bool cancel) {
+  EventListener listener;
+  listener.extension_id = extension_id;
+  listener.sub_event_name = sub_event_name;
+
+  // The listener may have been removed (e.g. due to the process going away)
+  // before we got here.
+  std::set<EventListener>::iterator found =
+      listeners_[profile_id][event_name].find(listener);
+  if (found != listeners_[profile_id][event_name].end())
+    found->blocked_requests.erase(request_id);
+
+  DecrementBlockCount(request_id, cancel);
 }
 
 void ExtensionWebRequestEventRouter::AddEventListener(
+    ProfileId profile_id,
     const std::string& extension_id,
     const std::string& event_name,
     const std::string& sub_event_name,
@@ -260,12 +324,13 @@ void ExtensionWebRequestEventRouter::AddEventListener(
   listener.filter = filter;
   listener.extra_info_spec = extra_info_spec;
 
-  CHECK_EQ(listeners_[event_name].count(listener), 0u) <<
+  CHECK_EQ(listeners_[profile_id][event_name].count(listener), 0u) <<
       "extension=" << extension_id << " event=" << event_name;
-  listeners_[event_name].insert(listener);
+  listeners_[profile_id][event_name].insert(listener);
 }
 
 void ExtensionWebRequestEventRouter::RemoveEventListener(
+    ProfileId profile_id,
     const std::string& extension_id,
     const std::string& sub_event_name) {
   size_t slash_sep = sub_event_name.find('/');
@@ -278,16 +343,29 @@ void ExtensionWebRequestEventRouter::RemoveEventListener(
   listener.extension_id = extension_id;
   listener.sub_event_name = sub_event_name;
 
-  CHECK_EQ(listeners_[event_name].count(listener), 1u) <<
+  CHECK_EQ(listeners_[profile_id][event_name].count(listener), 1u) <<
       "extension=" << extension_id << " event=" << event_name;
-  listeners_[event_name].erase(listener);
+
+  // Unblock any request that this event listener may have been blocking.
+  std::set<EventListener>::iterator found =
+      listeners_[profile_id][event_name].find(listener);
+  for (std::set<uint64>::iterator it = found->blocked_requests.begin();
+       it != found->blocked_requests.end(); ++it) {
+    DecrementBlockCount(*it, false);
+  }
+
+  listeners_[profile_id][event_name].erase(listener);
 }
 
 std::vector<const ExtensionWebRequestEventRouter::EventListener*>
 ExtensionWebRequestEventRouter::GetMatchingListeners(
-    const std::string& event_name, const GURL& url) {
+    ProfileId profile_id,
+    const std::string& event_name,
+    const GURL& url) {
+  // TODO(mpcomplete): handle profile_id == invalid (should collect all
+  // listeners).
   std::vector<const EventListener*> matching_listeners;
-  std::set<EventListener>& listeners = listeners_[event_name];
+  std::set<EventListener>& listeners = listeners_[profile_id][event_name];
   for (std::set<EventListener>::iterator it = listeners.begin();
        it != listeners.end(); ++it) {
     if (it->filter.urls.is_empty() || it->filter.urls.ContainsURL(url))
@@ -296,6 +374,27 @@ ExtensionWebRequestEventRouter::GetMatchingListeners(
   return matching_listeners;
 }
 
+void ExtensionWebRequestEventRouter::DecrementBlockCount(uint64 request_id,
+                                                         bool cancel) {
+  // It's possible that this request was already cancelled by a previous event
+  // handler. If so, ignore this response.
+  if (blocked_requests_.find(request_id) == blocked_requests_.end())
+    return;
+
+  BlockedRequest& blocked_request = blocked_requests_[request_id];
+  int num_handlers_blocking = --blocked_request.num_handlers_blocking;
+  CHECK_GE(num_handlers_blocking, 0);
+
+  HISTOGRAM_TIMES("Extensions.NetworkDelay",
+                   base::Time::Now() - blocked_request.request_time);
+
+  if (num_handlers_blocking == 0 || cancel) {
+    CHECK(blocked_request.callback);
+    blocked_request.callback->Run(cancel ? net::ERR_EMPTY_RESPONSE : net::OK);
+    blocked_requests_.erase(request_id);
+  }
+}
+
 bool WebRequestAddEventListener::RunImpl() {
   // Argument 0 is the callback, which we don't use here.
 
@@ -325,7 +424,40 @@ bool WebRequestAddEventListener::RunImpl() {
       BrowserThread::IO, FROM_HERE,
       NewRunnableFunction(
           &AddEventListenerOnIOThread,
-          extension_id(), event_name, sub_event_name, filter, extra_info_spec));
+          profile()->GetRuntimeId(), extension_id(),
+          event_name, sub_event_name, filter, extra_info_spec));
+
+  return true;
+}
+
+bool WebRequestEventHandled::RunImpl() {
+  std::string event_name;
+  EXTENSION_FUNCTION_VALIDATE(args_->GetString(0, &event_name));
+
+  std::string sub_event_name;
+  EXTENSION_FUNCTION_VALIDATE(args_->GetString(1, &sub_event_name));
+
+  std::string request_id_str;
+  EXTENSION_FUNCTION_VALIDATE(args_->GetString(2, &request_id_str));
+  // TODO(mpcomplete): string-to-uint64?
+  int64 request_id;
+  EXTENSION_FUNCTION_VALIDATE(base::StringToInt64(request_id_str, &request_id));
+
+  bool cancel = false;
+  if (HasOptionalArgument(3)) {
+    DictionaryValue* value = NULL;
+    EXTENSION_FUNCTION_VALIDATE(args_->GetDictionary(3, &value));
+
+    if (value->HasKey("cancel"))
+      EXTENSION_FUNCTION_VALIDATE(value->GetBoolean("cancel", &cancel));
+  }
+
+  BrowserThread::PostTask(
+      BrowserThread::IO, FROM_HERE,
+      NewRunnableFunction(
+          &EventHandledOnIOThread,
+          profile()->GetRuntimeId(), extension_id(),
+          event_name, sub_event_name, request_id, cancel));
 
   return true;
 }
diff --git a/chrome/browser/extensions/extension_webrequest_api.h b/chrome/browser/extensions/extension_webrequest_api.h
index f04edc9..0cd52a3 100644
--- a/chrome/browser/extensions/extension_webrequest_api.h
+++ b/chrome/browser/extensions/extension_webrequest_api.h
@@ -12,13 +12,18 @@
 #include <vector>
 
 #include "base/singleton.h"
-#include "ipc/ipc_message.h"
 #include "chrome/browser/extensions/extension_function.h"
 #include "chrome/browser/profiles/profile.h"
+#include "ipc/ipc_message.h"
+#include "net/base/completion_callback.h"
 
 class ExtensionEventRouterForwarder;
 class GURL;
 
+namespace net {
+class URLRequest;
+}
+
 // This class observes network events and routes them to the appropriate
 // extensions listening to those events. All methods must be called on the IO
 // thread unless otherwise specified.
@@ -29,24 +34,29 @@ class ExtensionWebRequestEventRouter {
 
   static ExtensionWebRequestEventRouter* GetInstance();
 
-  // Removes the listener for the given sub-event. Can be called on the UI
-  // thread.
-  static void RemoveEventListenerOnUIThread(
-      const std::string& extension_id,
-      const std::string& sub_event_name);
+  // Dispatches the OnBeforeRequest event to any extensions whose filters match
+  // the given request. Returns true if an extension wants to pause the request.
+  bool OnBeforeRequest(ProfileId profile_id,
+                       ExtensionEventRouterForwarder* event_router,
+                       net::URLRequest* request,
+                       net::CompletionCallback* callback);
 
-  // TODO(mpcomplete): additional params
-  void OnBeforeRequest(
-      ExtensionEventRouterForwarder* event_router,
+  // Called when an event listener handles a blocking event and responds.
+  // TODO(mpcomplete): modify request
+  void OnEventHandled(
       ProfileId profile_id,
-      const GURL& url,
-      const std::string& method);
+      const std::string& extension_id,
+      const std::string& event_name,
+      const std::string& sub_event_name,
+      uint64 request_id,
+      bool cancel);
 
   // Adds a listener to the given event. |event_name| specifies the event being
   // listened to. |sub_event_name| is an internal event uniquely generated in
   // the extension process to correspond to the given filter and
   // extra_info_spec.
   void AddEventListener(
+      ProfileId profile_id,
       const std::string& extension_id,
       const std::string& event_name,
       const std::string& sub_event_name,
@@ -55,13 +65,17 @@ class ExtensionWebRequestEventRouter {
 
   // Removes the listener for the given sub-event.
   void RemoveEventListener(
+      ProfileId profile_id,
       const std::string& extension_id,
       const std::string& sub_event_name);
 
  private:
   friend struct DefaultSingletonTraits<ExtensionWebRequestEventRouter>;
   struct EventListener;
-  typedef std::map<std::string, std::set<EventListener> > ListenerMap;
+  struct BlockedRequest;
+  typedef std::map<std::string, std::set<EventListener> > ListenerMapForProfile;
+  typedef std::map<ProfileId, ListenerMapForProfile> ListenerMap;
+  typedef std::map<uint64, BlockedRequest> BlockedRequestMap;
 
   ExtensionWebRequestEventRouter();
   ~ExtensionWebRequestEventRouter();
@@ -69,12 +83,21 @@ class ExtensionWebRequestEventRouter {
   // Returns a list of event listeners that care about the given event, based
   // on their filter parameters.
   std::vector<const EventListener*> GetMatchingListeners(
-      const std::string& event_name, const GURL& url);
+      ProfileId profile_id, const std::string& event_name, const GURL& url);
 
-  // A map between an event name and a set of extensions that are listening
-  // to that event.
+  // Decrements the count of event handlers blocking the given request. When the
+  // count reaches 0 (or immediately if the request is being cancelled), we
+  // stop blocking the request and either resume or cancel it.
+  void DecrementBlockCount(uint64 request_id, bool cancel);
+
+  // A map for each profile that maps an event name to a set of extensions that
+  // are listening to that event.
   ListenerMap listeners_;
 
+  // A map of network requests that are waiting for at least one event handler
+  // to respond.
+  BlockedRequestMap blocked_requests_;
+
   DISALLOW_COPY_AND_ASSIGN(ExtensionWebRequestEventRouter);
 };
 
@@ -84,4 +107,10 @@ class WebRequestAddEventListener : public SyncExtensionFunction {
   DECLARE_EXTENSION_FUNCTION_NAME("experimental.webRequest.addEventListener");
 };
 
+class WebRequestEventHandled : public SyncExtensionFunction {
+ public:
+  virtual bool RunImpl();
+  DECLARE_EXTENSION_FUNCTION_NAME("experimental.webRequest.eventHandled");
+};
+
 #endif  // CHROME_BROWSER_EXTENSIONS_EXTENSION_WEBREQUEST_API_H_
diff --git a/chrome/browser/io_thread.cc b/chrome/browser/io_thread.cc
index 9a0e035..4324b60 100644
--- a/chrome/browser/io_thread.cc
+++ b/chrome/browser/io_thread.cc
@@ -336,7 +336,7 @@ void IOThread::Init() {
   globals_->extension_event_router_forwarder =
       extension_event_router_forwarder_;
   globals_->system_network_delegate.reset(new ChromeNetworkDelegate(
-        extension_event_router_forwarder_, Profile::kInvalidProfileId));
+      extension_event_router_forwarder_, Profile::kInvalidProfileId));
   globals_->host_resolver.reset(
       CreateGlobalHostResolver(net_log_));
   globals_->cert_verifier.reset(new net::CertVerifier);
diff --git a/chrome/browser/net/chrome_network_delegate.cc b/chrome/browser/net/chrome_network_delegate.cc
index 59fb2e6..8fa34b0 100644
--- a/chrome/browser/net/chrome_network_delegate.cc
+++ b/chrome/browser/net/chrome_network_delegate.cc
@@ -41,9 +41,10 @@ ChromeNetworkDelegate::ChromeNetworkDelegate(
 
 ChromeNetworkDelegate::~ChromeNetworkDelegate() {}
 
-void ChromeNetworkDelegate::OnBeforeURLRequest(net::URLRequest* request) {
-  ExtensionWebRequestEventRouter::GetInstance()->OnBeforeRequest(
-      event_router_.get(), profile_id_, request->url(), request->method());
+bool ChromeNetworkDelegate::OnBeforeURLRequest(
+    net::URLRequest* request, net::CompletionCallback* callback) {
+  return ExtensionWebRequestEventRouter::GetInstance()->OnBeforeRequest(
+      profile_id_, event_router_.get(), request, callback);
 }
 
 void ChromeNetworkDelegate::OnSendHttpRequest(
diff --git a/chrome/browser/net/chrome_network_delegate.h b/chrome/browser/net/chrome_network_delegate.h
index 5b3fb15..2f2f0ea 100644
--- a/chrome/browser/net/chrome_network_delegate.h
+++ b/chrome/browser/net/chrome_network_delegate.h
@@ -17,8 +17,8 @@ class ExtensionEventRouterForwarder;
 // add hooks into the network stack.
 class ChromeNetworkDelegate : public net::NetworkDelegate {
  public:
-  // If |profile| is NULL, events will be broadcasted to all profiles,
-  // otherwise, they will be only send to the specified profile.
+  // If |profile_id| is the invalid profile, events will be broadcasted to all
+  // profiles, otherwise, they will only be sent to the specified profile.
   explicit ChromeNetworkDelegate(
       ExtensionEventRouterForwarder* event_router,
       ProfileId profile_id);
@@ -26,7 +26,8 @@ class ChromeNetworkDelegate : public net::NetworkDelegate {
 
  private:
   // NetworkDelegate methods:
-  virtual void OnBeforeURLRequest(net::URLRequest* request);
+  virtual bool OnBeforeURLRequest(net::URLRequest* request,
+                                  net::CompletionCallback* callback);
   virtual void OnSendHttpRequest(net::HttpRequestHeaders* headers);
   virtual void OnResponseStarted(net::URLRequest* request);
   virtual void OnReadCompleted(net::URLRequest* request, int bytes_read);
diff --git a/chrome/browser/profiles/profile_impl.cc b/chrome/browser/profiles/profile_impl.cc
index 0d4d077..913f6d5 100644
--- a/chrome/browser/profiles/profile_impl.cc
+++ b/chrome/browser/profiles/profile_impl.cc
@@ -836,14 +836,11 @@ URLRequestContextGetter* ProfileImpl::GetRequestContextForExtensions() {
 
 void ProfileImpl::RegisterExtensionWithRequestContexts(
     const Extension* extension) {
-  // AddRef to ensure the data lives until the other thread gets it. Balanced in
-  // OnNewExtensions.
-  extension->AddRef();
   BrowserThread::PostTask(
       BrowserThread::IO, FROM_HERE,
       NewRunnableMethod(extension_info_map_.get(),
                         &ExtensionInfoMap::AddExtension,
-                        extension));
+                        make_scoped_refptr(extension)));
 }
 
 void ProfileImpl::UnregisterExtensionWithRequestContexts(
diff --git a/chrome/common/extensions/api/extension_api.json b/chrome/common/extensions/api/extension_api.json
index d23f1ae..a4a53f5 100644
--- a/chrome/common/extensions/api/extension_api.json
+++ b/chrome/common/extensions/api/extension_api.json
@@ -3337,7 +3337,7 @@
               "tabId": {"type": "integer", "description": "The ID of the tab in which the navigation is about to occur."},
               "url": {"type": "string"},
               "frameId": {"type": "integer", "description": "0 indicates the navigation happens in the tab content window; positive value indicates navigation in a subframe. Frame IDs are unique within a tab."},
-              "requestId": {"type": "integer", "description": "The ID of the request to retrieve the document of this navigation. Note that this event is fired prior to the corresponding chrome.experimental.webRequest.onBeforeRequest."},
+              "requestId": {"type": "string", "description": "The ID of the request to retrieve the document of this navigation. Note that this event is fired prior to the corresponding chrome.experimental.webRequest.onBeforeRequest."},
               "timeStamp": {"type": "number", "description": "The time when the browser was about to start the navigation, in milliseconds since the epoch."}
             }
           }
@@ -3479,12 +3479,31 @@
             "description": "Array of extra information that should be passed to the listener function.",
             "items": {
               "type": "string",
-              "enum": ["requestLine", "requestHeaders", "statusLine", "responseHeaders", "redirectRequestLine", "redirectRequestHeaders"]
+              "enum": ["requestLine", "requestHeaders", "statusLine", "responseHeaders", "redirectRequestLine", "redirectRequestHeaders", "blocking"]
             }
           },
           {"type": "string", "name": "eventName"},
           {"type": "string", "name": "subEventName"}
         ]
+      },
+      {
+        "name": "eventHandled",
+        "nodoc": true,
+        "type": "function",
+        "description": "Used internally to send a response for a blocked event.",
+        "parameters": [
+          {"type": "string", "name": "eventName"},
+          {"type": "string", "name": "subEventName"},
+          {"type": "string", "name": "requestId"},
+          {
+            "type": "object",
+            "name": "response",
+            "optional": true,
+            "properties": {
+              "cancel": {"type": "boolean", "optional": true}
+            }
+          }
+        ]
       }
     ],
     "events": [
@@ -3497,7 +3516,7 @@
             "type": "object",
             "name": "details",
             "properties": {
-              "requestId": {"type": "integer", "description": "The ID of the request. Request IDs are unique within a browser session. As a result, they could be used to relate different events of the same request."},
+              "requestId": {"type": "string", "description": "The ID of the request. Request IDs are unique within a browser session. As a result, they could be used to relate different events of the same request."},
               "url": {"type": "string"},
               "method": {"type": "string", "description": "Standard HTTP method."},
               "tabId": {"type": "integer", "description": "The ID of the tab in which the request takes place. Set to null if the request isn't related to a tab."},
@@ -3516,7 +3535,7 @@
             "type": "object",
             "name": "details",
             "properties": {
-              "requestId": {"type": "integer", "description": "The ID of the request."},
+              "requestId": {"type": "string", "description": "The ID of the request."},
               "url": {"type": "string"},
               "ip": {"type": "string", "description": "The server IP address that is actually connected to. Note that it may be a literal IPv6 address."},
               "timeStamp": {"type": "number", "description": "The time when the browser finished sending the request, in milliseconds since the epoch."}
@@ -3533,7 +3552,7 @@
             "type": "object",
             "name": "details",
             "properties": {
-              "requestId": {"type": "integer", "description": "The ID of the request."},
+              "requestId": {"type": "string", "description": "The ID of the request."},
               "url": {"type": "string"},
               "statusCode": {"type": "integer", "description": "Standard HTTP status code returned by the server."},
               "timeStamp": {"type": "number", "description": "The time when the status line and response headers were received, in milliseconds since the epoch."}
@@ -3550,7 +3569,7 @@
             "type": "object",
             "name": "details",
             "properties": {
-              "requestId": {"type": "integer", "description": "The ID of the request."},
+              "requestId": {"type": "string", "description": "The ID of the request."},
               "url": {"type": "string", "description": "The URL of the current request."},
               "statusCode": {"type": "integer", "description": "Standard HTTP status code returned by the server."},
               "redirectUrl": {"type": "string", "description": "The new URL."},
@@ -3568,7 +3587,7 @@
             "type": "object",
             "name": "details",
             "properties": {
-              "requestId": {"type": "integer", "description": "The ID of the request."},
+              "requestId": {"type": "string", "description": "The ID of the request."},
               "url": {"type": "string", "description": "The URL of the current request."},
               "statusCode": {"type": "integer", "description": "Standard HTTP status code returned by the server."},
               "timeStamp": {"type": "number", "description": "The time when the response was received completely, in milliseconds since the epoch."}
@@ -3585,7 +3604,7 @@
             "type": "object",
             "name": "details",
             "properties": {
-              "requestId": {"type": "integer", "description": "The ID of the request."},
+              "requestId": {"type": "string", "description": "The ID of the request."},
               "url": {"type": "string", "description": "The URL of the current request."},
               "error": {"type": "string", "description": "The error description."},
               "timeStamp": {"type": "number", "description": "The time when the error occurred, in milliseconds since the epoch."}
diff --git a/chrome/common/extensions/docs/examples/extensions/imageinfo.zip b/chrome/common/extensions/docs/examples/extensions/imageinfo.zip
index 7d14906..4a61c1d 100644
--- a/chrome/common/extensions/docs/examples/extensions/imageinfo.zip
+++ b/chrome/common/extensions/docs/examples/extensions/imageinfo.zip
diff --git a/chrome/common/extensions/docs/experimental.webNavigation.html b/chrome/common/extensions/docs/experimental.webNavigation.html
index 7d733d1..9b16346 100644
--- a/chrome/common/extensions/docs/experimental.webNavigation.html
+++ b/chrome/common/extensions/docs/experimental.webNavigation.html
@@ -717,7 +717,7 @@
                         <span style="display: none; ">
                           array of <span><span></span></span>
                         </span>
-                        <span>integer</span>
+                        <span>string</span>
                         <span style="display: none; "></span>
                       </span>
                     </span>
diff --git a/chrome/common/extensions/docs/experimental.webRequest.html b/chrome/common/extensions/docs/experimental.webRequest.html
index 0e11c39..1f2fbbc 100644
--- a/chrome/common/extensions/docs/experimental.webRequest.html
+++ b/chrome/common/extensions/docs/experimental.webRequest.html
@@ -281,6 +281,8 @@
                     <ol>
                       <li style="display: none; ">
                         <a href="#method-anchor">methodName</a>
+                      </li><li style="display: none; ">
+                        <a href="#method-anchor">methodName</a>
                       </li>
                     </ol>
                   </li>
@@ -419,6 +421,72 @@
                 </p>
               </div> <!-- /description -->
 
+            </div><div class="apiItem" style="display: none; ">
+              <a></a> <!-- method-anchor -->
+              <h4>method name</h4>
+
+              <div class="summary"><span>void</span>
+                  <!-- Note: intentionally longer 80 columns -->
+                  <span>chrome.module.methodName</span>(<span><span>, </span><span></span>
+                      <var><span></span></var></span>)</div>
+
+              <div class="description">
+                <p class="todo">Undocumented.</p>
+                <p>
+                  A description from the json schema def of the function goes here.
+                </p>
+
+                <!-- PARAMETERS -->
+                <h4>Parameters</h4>
+                <dl>
+                  <div>
+                    <div>
+                    </div>
+                  </div>
+                </dl>
+
+                <!-- RETURNS -->
+                <h4>Returns</h4>
+                <dl>
+                  <div>
+                    <div>
+                    </div>
+                  </div>
+                </dl>
+
+                <!-- CALLBACK -->
+                <div>
+                  <div>
+                  <h4>Callback function</h4>
+                  <p>
+                    The callback <em>parameter</em> should specify a function
+                    that looks like this:
+                  </p>
+                  <p>
+                    If you specify the <em>callback</em> parameter, it should
+                    specify a function that looks like this:
+                  </p>
+
+                  <!-- Note: intentionally longer 80 columns -->
+                  <pre>function(<span>Type param1, Type param2</span>) <span class="subdued">{...}</span>;</pre>
+                  <dl>
+                    <div>
+                      <div>
+                      </div>
+                    </div>
+                  </dl>
+                  </div>
+                </div>
+
+                <!-- MIN_VERSION -->
+                <p>
+                  This function was added in version <b><span></span></b>.
+                  If you require this function, the manifest key
+                  <a href="manifest.html#minimum_chrome_version">minimum_chrome_version</a>
+                  can ensure that your extension won't be run in an earlier browser version.
+                </p>
+              </div> <!-- /description -->
+
             </div>  <!-- /apiItem -->
 
           </div>  <!-- /apiGroup -->
@@ -511,7 +579,7 @@
                         <span style="display: none; ">
                           array of <span><span></span></span>
                         </span>
-                        <span>integer</span>
+                        <span>string</span>
                         <span style="display: none; "></span>
                       </span>
                     </span>
@@ -940,7 +1008,7 @@
                         <span style="display: none; ">
                           array of <span><span></span></span>
                         </span>
-                        <span>integer</span>
+                        <span>string</span>
                         <span style="display: none; "></span>
                       </span>
                     </span>
@@ -1439,7 +1507,7 @@
                         <span style="display: none; ">
                           array of <span><span></span></span>
                         </span>
-                        <span>integer</span>
+                        <span>string</span>
                         <span style="display: none; "></span>
                       </span>
                     </span>
@@ -1800,7 +1868,7 @@
                         <span style="display: none; ">
                           array of <span><span></span></span>
                         </span>
-                        <span>integer</span>
+                        <span>string</span>
                         <span style="display: none; "></span>
                       </span>
                     </span>
@@ -2161,7 +2229,7 @@
                         <span style="display: none; ">
                           array of <span><span></span></span>
                         </span>
-                        <span>integer</span>
+                        <span>string</span>
                         <span style="display: none; "></span>
                       </span>
                     </span>
@@ -2524,7 +2592,7 @@
                         <span style="display: none; ">
                           array of <span><span></span></span>
                         </span>
-                        <span>integer</span>
+                        <span>string</span>
                         <span style="display: none; "></span>
                       </span>
                     </span>
diff --git a/chrome/common/extensions/docs/samples.json b/chrome/common/extensions/docs/samples.json
index 9a62535..2aad896 100644
--- a/chrome/common/extensions/docs/samples.json
+++ b/chrome/common/extensions/docs/samples.json
@@ -65,6 +65,7 @@
     "chrome.experimental.webNavigation.onDOMContentLoaded": "experimental.webNavigation.html#event-onDOMContentLoaded", 
     "chrome.experimental.webNavigation.onErrorOccurred": "experimental.webNavigation.html#event-onErrorOccurred", 
     "chrome.experimental.webRequest.addEventListener": "experimental.webRequest.html#method-addEventListener", 
+    "chrome.experimental.webRequest.eventHandled": "experimental.webRequest.html#method-eventHandled", 
     "chrome.experimental.webRequest.onBeforeRedirect": "experimental.webRequest.html#event-onBeforeRedirect", 
     "chrome.experimental.webRequest.onBeforeRequest": "experimental.webRequest.html#event-onBeforeRequest", 
     "chrome.experimental.webRequest.onCompleted": "experimental.webRequest.html#event-onCompleted", 
diff --git a/chrome/renderer/resources/event_bindings.js b/chrome/renderer/resources/event_bindings.js
index 2b8cce8..05ed65d 100644
--- a/chrome/renderer/resources/event_bindings.js
+++ b/chrome/renderer/resources/event_bindings.js
@@ -165,7 +165,8 @@ var chrome = chrome || {};
       try {
         this.listeners_[i].apply(null, args);
       } catch (e) {
-        console.error(e);
+        console.error("Error in event handler for '" + this.eventName_ +
+                      "': " + e);
       }
     }
   };
diff --git a/chrome/renderer/resources/extension_process_bindings.js b/chrome/renderer/resources/extension_process_bindings.js
index 0d97ced8..ce1b21d 100644
--- a/chrome/renderer/resources/extension_process_bindings.js
+++ b/chrome/renderer/resources/extension_process_bindings.js
@@ -259,6 +259,7 @@ var chrome = chrome || {};
     this.eventName_ = eventName;
     this.argSchemas_ = opt_argSchemas;
     this.subEvents_ = [];
+    this.callbackMap_ = {};
   };
 
   // Registers a callback to be called when this event is dispatched. If
@@ -275,24 +276,43 @@ var chrome = chrome || {};
 
     var subEvent = new chrome.Event(subEventName, this.argSchemas_);
     this.subEvents_.push(subEvent);
-    subEvent.addListener(cb);
+    var subEventCallback = cb;
+    if (opt_extraInfo && opt_extraInfo.indexOf("blocking") >= 0) {
+      var eventName = this.eventName_;
+      subEventCallback = function() {
+        var requestId = arguments[0].requestId;
+        try {
+          var result = cb.apply(null, arguments);
+          chrome.experimental.webRequest.eventHandled(
+              eventName, subEventName, requestId, result);
+        } catch (e) {
+          chrome.experimental.webRequest.eventHandled(
+              eventName, subEventName, requestId);
+          throw e;
+        }
+      };
+    }
+    this.callbackMap_[cb] = subEventCallback;
+    subEvent.addListener(subEventCallback);
   };
 
   // Unregisters a callback.
   chrome.WebRequestEvent.prototype.removeListener = function(cb) {
     var idx = this.findListener_(cb);
-    if (idx >= -1) {
+    if (idx < 0) {
       return;
     }
 
-    this.subEvents_[idx].removeListener(cb);
+    var subEventCallback = this.callbackMap_[cb];
+    this.subEvents_[idx].removeListener(subEventCallback);
     if (!this.subEvents_[idx].hasListeners())
       this.subEvents_.splice(idx, 1);
   };
 
   chrome.WebRequestEvent.prototype.findListener_ = function(cb) {
+    var subEventCallback = this.callbackMap_[cb];
     for (var i = 0; i < this.subEvents_.length; i++) {
-      if (this.subEvents_[i].findListener_(cb) > -1)
+      if (this.subEvents_[i].findListener_(subEventCallback) > -1)
         return i;
     }
 
diff --git a/chrome/test/data/extensions/api_test/webnavigation/clientRedirect/tests.js b/chrome/test/data/extensions/api_test/webnavigation/clientRedirect/tests.js
index 6cb9510..1b9094e 100644
--- a/chrome/test/data/extensions/api_test/webnavigation/clientRedirect/tests.js
+++ b/chrome/test/data/extensions/api_test/webnavigation/clientRedirect/tests.js
@@ -10,7 +10,7 @@ function runTests() {
         expect([
           [ "onBeforeNavigate",
             { frameId: 0,
-              requestId: 0,
+              requestId: "0",
               tabId: 0,
               timeStamp: 0,
               url: getURL('a.html') }],
@@ -33,7 +33,7 @@ function runTests() {
               url: getURL('a.html') }],
           [ "onBeforeNavigate",
             { frameId: 0,
-              requestId: 0,
+              requestId: "0",
               tabId: 0,
               timeStamp: 0,
               url: getURL('b.html') }],
diff --git a/chrome/test/data/extensions/api_test/webnavigation/failures/tests.js b/chrome/test/data/extensions/api_test/webnavigation/failures/tests.js
index a7c2f87..99b97c5 100644
--- a/chrome/test/data/extensions/api_test/webnavigation/failures/tests.js
+++ b/chrome/test/data/extensions/api_test/webnavigation/failures/tests.js
@@ -9,7 +9,7 @@ function runTests() {
         expect([
           [ "onBeforeNavigate",
             { frameId: 0,
-              requestId: 0,
+              requestId: "0",
               tabId: 0,
               timeStamp: 0,
               url: getURL('nonexistant.html') }],
@@ -27,7 +27,7 @@ function runTests() {
         expect([
           [ "onBeforeNavigate",
             { frameId: 0,
-              requestId: 0,
+              requestId: "0",
               tabId: 0,
               timeStamp: 0,
               url: getURL('d.html') }],
@@ -40,7 +40,7 @@ function runTests() {
               url: getURL('d.html') }],
           [ "onBeforeNavigate",
             { frameId: 1,
-              requestId: 0,
+              requestId: "0",
               tabId: 0,
               timeStamp: 0,
               url: getURL('c.html') }],
@@ -68,7 +68,7 @@ function runTests() {
         expect([
           [ "onBeforeNavigate",
             { frameId: 0,
-              requestId: 0,
+              requestId: "0",
               tabId: 0,
               timeStamp: 0,
               url: getURL('a.html') }],
@@ -81,7 +81,7 @@ function runTests() {
               url: getURL('a.html') }],
           [ "onBeforeNavigate",
             { frameId: 1,
-              requestId: 0,
+              requestId: "0",
               tabId: 0,
               timeStamp: 0,
               url: getURL('b.html') }],
@@ -114,7 +114,7 @@ function runTests() {
               url: getURL('a.html') }],
           [ "onBeforeNavigate",
             { frameId: 1,
-              requestId: 0,
+              requestId: "0",
               tabId: 0,
               timeStamp: 0,
               url: getURL('c.html') }],
diff --git a/chrome/test/data/extensions/api_test/webnavigation/forwardBack/tests.js b/chrome/test/data/extensions/api_test/webnavigation/forwardBack/tests.js
index 575a77c..6b8da61 100644
--- a/chrome/test/data/extensions/api_test/webnavigation/forwardBack/tests.js
+++ b/chrome/test/data/extensions/api_test/webnavigation/forwardBack/tests.js
@@ -10,7 +10,7 @@ function runTests() {
         expect([
           [ "onBeforeNavigate",
             { frameId: 0,
-              requestId: 0,
+              requestId: "0",
               tabId: 0,
               timeStamp: 0,
               url: getURL('a.html') }],
@@ -33,7 +33,7 @@ function runTests() {
               url: getURL('a.html') }],
           [ "onBeforeNavigate",
             { frameId: 0,
-              requestId: 0,
+              requestId: "0",
               tabId: 0,
               timeStamp: 0,
               url: getURL('b.html') }],
@@ -56,7 +56,7 @@ function runTests() {
               url: getURL('b.html') }],
           [ "onBeforeNavigate",
             { frameId: 0,
-              requestId: 0,
+              requestId: "0",
               tabId: 0,
               timeStamp: 0,
               url: getURL('a.html') }],
diff --git a/chrome/test/data/extensions/api_test/webnavigation/iframe/tests.js b/chrome/test/data/extensions/api_test/webnavigation/iframe/tests.js
index 4ba7af6..6d526c8 100644
--- a/chrome/test/data/extensions/api_test/webnavigation/iframe/tests.js
+++ b/chrome/test/data/extensions/api_test/webnavigation/iframe/tests.js
@@ -10,7 +10,7 @@ function runTests() {
         expect([
           [ "onBeforeNavigate",
             { frameId: 0,
-              requestId: 0,
+              requestId: "0",
               tabId: 0,
               timeStamp: 0,
               url: getURL('a.html') }],
@@ -23,7 +23,7 @@ function runTests() {
               url: getURL('a.html') }],
           [ "onBeforeNavigate",
             { frameId: 1,
-              requestId: 0,
+              requestId: "0",
               tabId: 0,
               timeStamp: 0,
               url: getURL('b.html') }],
@@ -56,7 +56,7 @@ function runTests() {
               url: getURL('a.html') }],
           [ "onBeforeNavigate",
             { frameId: 1,
-              requestId: 0,
+              requestId: "0",
               tabId: 0,
               timeStamp: 0,
               url: getURL('c.html') }],
@@ -87,7 +87,7 @@ function runTests() {
         expect([
           [ "onBeforeNavigate",
             { frameId: 0,
-              requestId: 0,
+              requestId: "0",
               tabId: 0,
               timeStamp: 0,
               url: getURL('d.html') }],
@@ -100,7 +100,7 @@ function runTests() {
               url: getURL('d.html') }],
           [ "onBeforeNavigate",
             { frameId: 1,
-              requestId: 0,
+              requestId: "0",
               tabId: 0,
               timeStamp: 0,
               url: getURL('e.html') }],
@@ -123,7 +123,7 @@ function runTests() {
               url: getURL('e.html') }],
           [ "onBeforeNavigate",
             { frameId: 2,
-              requestId: 0,
+              requestId: "0",
               tabId: 0,
               timeStamp: 0,
               url: getURL('f.html') }],
@@ -156,7 +156,7 @@ function runTests() {
               url: getURL('d.html') }],
           [ "onBeforeNavigate",
             { frameId: 2,
-              requestId: 0,
+              requestId: "0",
               tabId: 0,
               timeStamp: 0,
               url: getURL('g.html') }],
diff --git a/chrome/test/data/extensions/api_test/webnavigation/openTab/tests.js b/chrome/test/data/extensions/api_test/webnavigation/openTab/tests.js
index a35b60a..d35725c 100644
--- a/chrome/test/data/extensions/api_test/webnavigation/openTab/tests.js
+++ b/chrome/test/data/extensions/api_test/webnavigation/openTab/tests.js
@@ -9,7 +9,7 @@ function runTests() {
         expect([
           [ "onBeforeNavigate",
             { frameId: 0,
-              requestId: 0,
+              requestId: "0",
               tabId: 0,
               timeStamp: 0,
               url: getURL('a.html') }],
@@ -37,7 +37,7 @@ function runTests() {
               url: getURL('b.html') }],
           [ "onBeforeNavigate",
             { frameId: 0,
-              requestId: 0,
+              requestId: "0",
               tabId: 1,
               timeStamp: 0,
               url: getURL('b.html') }],
@@ -66,7 +66,7 @@ function runTests() {
         expect([
           [ "onBeforeNavigate",
             { frameId: 0,
-              requestId: 0,
+              requestId: "0",
               tabId: 0,
               timeStamp: 0,
               url: getURL('c.html') }],
@@ -79,7 +79,7 @@ function runTests() {
               url: getURL('c.html') }],
           [ "onBeforeNavigate",
             { frameId: 1,
-              requestId: 0,
+              requestId: "0",
               tabId: 0,
               timeStamp: 0,
               url: getURL('a.html') }],
@@ -117,7 +117,7 @@ function runTests() {
               url: getURL('b.html') }],
           [ "onBeforeNavigate",
             { frameId: 0,
-              requestId: 0,
+              requestId: "0",
               tabId: 1,
               timeStamp: 0,
               url: getURL('b.html') }],
diff --git a/chrome/test/data/extensions/api_test/webnavigation/referenceFragment/tests.js b/chrome/test/data/extensions/api_test/webnavigation/referenceFragment/tests.js
index 5b9675e..4fb0341 100644
--- a/chrome/test/data/extensions/api_test/webnavigation/referenceFragment/tests.js
+++ b/chrome/test/data/extensions/api_test/webnavigation/referenceFragment/tests.js
@@ -9,7 +9,7 @@ function runTests() {
         expect([
           [ "onBeforeNavigate",
             { frameId: 0,
-              requestId: 0,
+              requestId: "0",
               tabId: 0,
               timeStamp: 0,
               url: getURL('a.html') }],
@@ -32,7 +32,7 @@ function runTests() {
               url: getURL('a.html') }],
           [ "onBeforeNavigate",
             { frameId: 0,
-              requestId: 0,
+              requestId: "0",
               tabId: 0,
               timeStamp: 0,
               url: getURL('a.html#anchor') }],
diff --git a/chrome/test/data/extensions/api_test/webnavigation/simpleLoad/tests.js b/chrome/test/data/extensions/api_test/webnavigation/simpleLoad/tests.js
index 377d38e..13e7126 100644
--- a/chrome/test/data/extensions/api_test/webnavigation/simpleLoad/tests.js
+++ b/chrome/test/data/extensions/api_test/webnavigation/simpleLoad/tests.js
@@ -9,7 +9,7 @@ function runTests() {
         expect([
           [ "onBeforeNavigate",
             { frameId: 0,
-              requestId: 0,
+              requestId: "0",
               tabId: 0,
               timeStamp: 0,
               url: getURL('a.html') }],
diff --git a/chrome/test/data/extensions/api_test/webrequest/events/test.html b/chrome/test/data/extensions/api_test/webrequest/events/test.html
index 1489e2e..83c1dba 100644
--- a/chrome/test/data/extensions/api_test/webrequest/events/test.html
+++ b/chrome/test/data/extensions/api_test/webrequest/events/test.html
@@ -2,12 +2,12 @@
 var getURL = chrome.extension.getURL;
 var expectedEventData;
 var capturedEventData;
-var captureFilteredEvents;
 
-function expect(data, filtered) {
+function expect(data, filter, extraInfoSpec) {
   expectedEventData = data;
   capturedEventData = [];
-  captureFilteredEvents = filtered;
+  removeListeners();
+  initListeners(filter, extraInfoSpec);
 }
 
 function checkExpectations() {
@@ -20,49 +20,66 @@ function checkExpectations() {
   chrome.test.succeed();
 }
 
-function captureEvent(name, details, isFiltered) {
+function captureEvent(name, details) {
   // TODO(mpcomplete): implement the rest of the parameters.
   delete details.requestId;
   delete details.tabId;
   delete details.timeStamp;
   delete details.type;
-  if (captureFilteredEvents == isFiltered)
-    capturedEventData.push([name, details]);
+  capturedEventData.push([name, details]);
   checkExpectations();
 }
 
-chrome.experimental.webRequest.onBeforeRequest.addListener(
-    function(details) {
-  captureEvent("onBeforeRequest", details);
-});
-chrome.experimental.webRequest.onRequestSent.addListener(
-    function(details) {
-  captureEvent("onRequestSent", details);
-});
-chrome.experimental.webRequest.onHeadersReceived.addListener(
-    function(details) {
-  captureEvent("onHeadersReceived", details);
-});
-chrome.experimental.webRequest.onBeforeRedirect.addListener(
-    function(details) {
-  captureEvent("onBeforeRedirect", details);
-});
-chrome.experimental.webRequest.onCompleted.addListener(
-    function(details) {
-  captureEvent("onCompleted", details);
-});
-chrome.experimental.webRequest.onErrorOccurred.addListener(
-    function(details) {
-  captureEvent("onErrorOccurred", details);
-});
+function initListeners(filter, extraInfoSpec) {
+  chrome.experimental.webRequest.onBeforeRequest.addListener(
+      function(details) {
+    captureEvent("onBeforeRequest", details);
+    return {cancel: true};  // no effect unless event is blocking.
+  }, filter, extraInfoSpec);
+  chrome.experimental.webRequest.onRequestSent.addListener(
+      function(details) {
+    captureEvent("onRequestSent", details);
+    return {cancel: true};
+  }, filter, extraInfoSpec);
+  chrome.experimental.webRequest.onHeadersReceived.addListener(
+      function(details) {
+    captureEvent("onHeadersReceived", details);
+    return {cancel: true};
+  }, filter, extraInfoSpec);
+  chrome.experimental.webRequest.onBeforeRedirect.addListener(
+      function(details) {
+    captureEvent("onBeforeRedirect", details);
+    return {cancel: true};
+  }, filter, extraInfoSpec);
+  chrome.experimental.webRequest.onCompleted.addListener(
+      function(details) {
+    captureEvent("onCompleted", details);
+    return {cancel: true};
+  }, filter, extraInfoSpec);
+  chrome.experimental.webRequest.onErrorOccurred.addListener(
+      function(details) {
+    captureEvent("onErrorOccurred", details);
+    return {cancel: true};
+  }, filter, extraInfoSpec);
+}
 
-// For filter tests.
-chrome.experimental.webRequest.onBeforeRequest.addListener(
-    function(details) {
-  captureEvent("onBeforeRequest", details, true);
-},
-    {urls: [getURL("simpleLoad/*")]}
-);
+function removeListeners() {
+  function helper(event) {
+    // Note: We're poking at the internal event data, but it's easier than
+    // the alternative. If this starts failing, we just need to update this
+    // helper.
+    for (var cb in event.callbackMap_) {
+      event.removeListener(cb);
+    }
+    chrome.test.assertEq(0, event.subEvents_.length);
+  }
+  helper(chrome.experimental.webRequest.onBeforeRequest);
+  helper(chrome.experimental.webRequest.onRequestSent);
+  helper(chrome.experimental.webRequest.onHeadersReceived);
+  helper(chrome.experimental.webRequest.onBeforeRedirect);
+  helper(chrome.experimental.webRequest.onCompleted);
+  helper(chrome.experimental.webRequest.onErrorOccurred);
+}
 
 chrome.tabs.getSelected(null, function(tab) {
   var tabId = tab.id;
@@ -108,6 +125,21 @@ chrome.tabs.getSelected(null, function(tab) {
       chrome.tabs.update(tabId, { url: getURL("complexLoad/a.html") });
     },
 
+    // Navigates to a page with subresources, with a blocking handler that
+    // cancels the page request. The page will not load, and we should not
+    // see the subresources.
+    function complexLoadBlocking() {
+      expect([
+        [ "onBeforeRequest",
+          {
+            method: "GET",
+            url: getURL("complexLoad/a.html")
+          }
+        ]
+      ], {}, ["blocking"]);
+      chrome.tabs.update(tabId, { url: getURL("complexLoad/a.html") });
+    },
+
     // Loads several resources, but should only see the simpleLoad
     // due to the filter.
     function simpleLoadFiltered() {
@@ -118,9 +150,9 @@ chrome.tabs.getSelected(null, function(tab) {
             url: getURL("simpleLoad/a.html")
           }
         ],
-      ], true);
+      ], {urls: [getURL("simpleLoad/*")]}, []);
       chrome.tabs.update(tabId, { url: getURL("complexLoad/a.html") });
-      chrome.tabs.update(tabId, { url: getURL("simpleLoad/a.html") });
+      chrome.tabs.create({ url: getURL("simpleLoad/a.html") });
     },
   ]);
 });
diff --git a/chrome/test/data/extensions/profiles/extension_webrequest/Default/Extensions/behllobkkfkfnphdnhnkndlbkcpglgmj/1.0.0.0/background.html b/chrome/test/data/extensions/profiles/extension_webrequest/Default/Extensions/behllobkkfkfnphdnhnkndlbkcpglgmj/1.0.0.0/background.html
new file mode 100644
index 0000000..09904d7
--- /dev/null
+++ b/chrome/test/data/extensions/profiles/extension_webrequest/Default/Extensions/behllobkkfkfnphdnhnkndlbkcpglgmj/1.0.0.0/background.html
@@ -0,0 +1,10 @@
+<script>
+var onBefore = chrome.experimental.webRequest.onBeforeRequest;
+onBefore.addListener(function(info) {
+  return {"cancel": false};
+}, {urls: ["http://*/*"]}, ['blocking']);
+var onBefore = chrome.experimental.webRequest.onBeforeRequest;
+onBefore.addListener(function(info) {
+  return {"cancel": false};
+}, {urls: ["file://*/*"]}, ['blocking']);
+</script>
diff --git a/chrome/test/data/extensions/profiles/extension_webrequest/Default/Extensions/behllobkkfkfnphdnhnkndlbkcpglgmj/1.0.0.0/manifest.json b/chrome/test/data/extensions/profiles/extension_webrequest/Default/Extensions/behllobkkfkfnphdnhnkndlbkcpglgmj/1.0.0.0/manifest.json
new file mode 100644
index 0000000..d134e26
--- /dev/null
+++ b/chrome/test/data/extensions/profiles/extension_webrequest/Default/Extensions/behllobkkfkfnphdnhnkndlbkcpglgmj/1.0.0.0/manifest.json
@@ -0,0 +1,7 @@
+{
+  "key": "MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDuUZGKCDbff6IRaxa4Pue7PPkxwPaNhGT3JEqppEsNWFjM80imEdqMbf3lrWqEfaHgaNku7nlpwPO1mu3/4Hr+XdNa5MhfnOnuPee4hyTLwOs3Vzz81wpbdzUxZSi2OmqMyI5oTaBYICfNHLwcuc65N5dbt6WKGeKgTpp4v7j7zwIDAQAB",
+  "version": "1.0.0.0",
+  "name": "Webrequest",
+  "permissions": ["experimental", "webRequest"],
+  "background_page": "background.html"
+}
diff --git a/chrome/test/data/extensions/profiles/extension_webrequest/Default/Preferences b/chrome/test/data/extensions/profiles/extension_webrequest/Default/Preferences
new file mode 100644
index 0000000..7810326
--- /dev/null
+++ b/chrome/test/data/extensions/profiles/extension_webrequest/Default/Preferences
@@ -0,0 +1,75 @@
+{
+   "browser": {
+      "window_placement": {
+         "bottom": 1150,
+         "left": 10,
+         "maximized": false,
+         "right": 955,
+         "top": 10,
+         "work_area_bottom": 1160,
+         "work_area_left": 0,
+         "work_area_right": 1920,
+         "work_area_top": 0
+      }
+   },
+   "countryid_at_install": 21843,
+   "dns_prefetching": {
+      "host_referral_list": [ 2 ],
+      "startup_list": [ 1 ]
+   },
+   "download": {
+      "directory_upgrade": true,
+      "extensions_to_open": ""
+   },
+   "extensions": {
+      "autoupdate": {
+         "next_check": "12943417068538765"
+      },
+      "chrome_url_overrides": {
+         "bookmarks": [ "chrome-extension://eemcgdkfndhakfknompkggombfjjjeno/main.html" ]
+      },
+      "settings": {
+         "behllobkkfkfnphdnhnkndlbkcpglgmj": {
+            "granted_permissions": {
+               "api": [ "experimental" ],
+               "full": false
+            },
+            "install_time": "12943416715915765",
+            "location": 1,
+            "manifest": {
+               "background_page": "background.html",
+               "key": "MIGfMA0GCSqGSIb3DQEBAQUAA4GNADCBiQKBgQDuUZGKCDbff6IRaxa4Pue7PPkxwPaNhGT3JEqppEsNWFjM80imEdqMbf3lrWqEfaHgaNku7nlpwPO1mu3/4Hr+XdNa5MhfnOnuPee4hyTLwOs3Vzz81wpbdzUxZSi2OmqMyI5oTaBYICfNHLwcuc65N5dbt6WKGeKgTpp4v7j7zwIDAQAB",
+               "name": "Webrequest",
+               "permissions": [ "experimental", "webRequest" ],
+               "version": "1.0.0.0"
+            },
+            "path": "behllobkkfkfnphdnhnkndlbkcpglgmj/1.0.0.0",
+            "state": 1
+         }
+      }
+   },
+   "google": {
+      "services": {
+         "username": ""
+      }
+   },
+   "ntp": {
+      "pref_version": 3,
+      "promo_resource_cache_update": "1298943121.229765"
+   },
+   "plugins": {
+      "enabled_internal_pdf3": true
+   },
+   "profile": {
+      "content_settings": {
+         "pref_version": 1
+      },
+      "exited_cleanly": true,
+      "id": "not-signed-in",
+      "name": "",
+      "nickname": ""
+   },
+   "tabs": {
+      "use_vertical_tabs": false
+   }
+}
diff --git a/chrome/test/page_cycler/page_cycler_test.cc b/chrome/test/page_cycler/page_cycler_test.cc
index 69f164b..5cabe96 100644
--- a/chrome/test/page_cycler/page_cycler_test.cc
+++ b/chrome/test/page_cycler/page_cycler_test.cc
@@ -178,6 +178,8 @@ class PageCyclerTest : public UIPerfTest {
     // Expose garbage collection for the page cycler tests.
     launch_arguments_.AppendSwitchASCII(switches::kJavaScriptFlags,
                                         "--expose_gc");
+    // Enable experimental extension APIs for webrequest tests.
+    launch_arguments_.AppendSwitch(switches::kEnableExperimentalExtensionApis);
 #if defined(OS_MACOSX)
     static rlim_t initial_fd_limit = GetFileDescriptorLimit();
     fd_limit_ = initial_fd_limit;
@@ -368,6 +370,9 @@ class PageCyclerExtensionTest : public PageCyclerTest {
   }
 };
 
+class PageCyclerExtensionWebRequestTest : public PageCyclerExtensionTest {
+};
+
 static FilePath GetDatabaseDataPath(const char* name) {
   FilePath test_path;
   PathService::Get(base::DIR_SOURCE_ROOT, &test_path);
@@ -550,11 +555,21 @@ TEST_F(PageCyclerExtensionTest, name##10) { \
   RunTest("times", "content_scripts10", "_extcs10", test, false); \
 }
 
+// This macro lets us define tests with an extension that listens to the
+// webrequest.onBeforeRequest. It measures the effect that a blocking event
+// for every request has on page cycle time.
+#define PAGE_CYCLER_EXTENSIONS_WEBREQUEST_FILE_TESTS(test, name) \
+TEST_F(PageCyclerExtensionWebRequestTest, name) { \
+  RunTest("times", "extension_webrequest", "_extwr", test, false); \
+}
+
 // file-URL tests
 PAGE_CYCLER_FILE_TESTS("moz", MozFile);
 PAGE_CYCLER_EXTENSIONS_FILE_TESTS("moz", MozFile);
+PAGE_CYCLER_EXTENSIONS_WEBREQUEST_FILE_TESTS("moz", MozFile)
 PAGE_CYCLER_FILE_TESTS("intl1", Intl1File);
 PAGE_CYCLER_FILE_TESTS("intl2", Intl2File);
+PAGE_CYCLER_EXTENSIONS_WEBREQUEST_FILE_TESTS("intl2", Intl2File);
 PAGE_CYCLER_FILE_TESTS("dom", DomFile);
 PAGE_CYCLER_FILE_TESTS("dhtml", DhtmlFile);
 PAGE_CYCLER_FILE_TESTS("morejs", MorejsFile);
diff --git a/net/base/net_log_event_type_list.h b/net/base/net_log_event_type_list.h
index ec72cb4..fa96247 100644
--- a/net/base/net_log_event_type_list.h
+++ b/net/base/net_log_event_type_list.h
@@ -497,6 +497,10 @@ EVENT_TYPE(URL_REQUEST_START_JOB)
 //   }
 EVENT_TYPE(URL_REQUEST_REDIRECTED)
 
+// Measures the time a net::URLRequest is blocked waiting for an extension to
+// respond to the onBefoteRequest extension event.
+EVENT_TYPE(URL_REQUEST_BLOCKED_ON_EXTENSION)
+
 // ------------------------------------------------------------------------
 // HttpCache
 // ------------------------------------------------------------------------
diff --git a/net/base/network_delegate.cc b/net/base/network_delegate.cc
index b00e671..b7ecd44 100644
--- a/net/base/network_delegate.cc
+++ b/net/base/network_delegate.cc
@@ -8,10 +8,12 @@
 
 namespace net {
 
-void NetworkDelegate::NotifyBeforeURLRequest(URLRequest* request) {
+bool NetworkDelegate::NotifyBeforeURLRequest(URLRequest* request,
+                                             CompletionCallback* callback) {
   DCHECK(CalledOnValidThread());
   DCHECK(request);
-  OnBeforeURLRequest(request);
+  DCHECK(callback);
+  return OnBeforeURLRequest(request, callback);
 }
 
 void NetworkDelegate::NotifySendHttpRequest(HttpRequestHeaders* headers) {
diff --git a/net/base/network_delegate.h b/net/base/network_delegate.h
index c4f2b65..7ffa1c3 100644
--- a/net/base/network_delegate.h
+++ b/net/base/network_delegate.h
@@ -7,6 +7,7 @@
 #pragma once
 
 #include "base/threading/non_thread_safe.h"
+#include "net/base/completion_callback.h"
 
 namespace net {
 
@@ -30,7 +31,8 @@ class NetworkDelegate : public base::NonThreadSafe {
   // Notification interface called by the network stack. Note that these
   // functions mostly forward to the private virtuals. They also add some sanity
   // checking on parameters.
-  void NotifyBeforeURLRequest(URLRequest* request);
+  bool NotifyBeforeURLRequest(URLRequest* request,
+                              CompletionCallback* callback);
   void NotifySendHttpRequest(HttpRequestHeaders* headers);
   void NotifyResponseStarted(URLRequest* request);
   void NotifyReadCompleted(URLRequest* request, int bytes_read);
@@ -41,7 +43,8 @@ class NetworkDelegate : public base::NonThreadSafe {
   // member function, which will perform basic sanity checking.
 
   // Called before a request is sent.
-  virtual void OnBeforeURLRequest(URLRequest* request) = 0;
+  virtual bool OnBeforeURLRequest(URLRequest* request,
+                                  CompletionCallback* callback) = 0;
 
   // Called right before the HTTP headers are sent.  Allows the delegate to
   // read/write |headers| before they get sent out.
diff --git a/net/url_request/url_request.cc b/net/url_request/url_request.cc
index 5af99ea..229611ca 100644
--- a/net/url_request/url_request.cc
+++ b/net/url_request/url_request.cc
@@ -19,6 +19,7 @@
 #include "net/http/http_response_headers.h"
 #include "net/http/http_util.h"
 #include "net/url_request/url_request_context.h"
+#include "net/url_request/url_request_error_job.h"
 #include "net/url_request/url_request_job.h"
 #include "net/url_request/url_request_job_manager.h"
 #include "net/url_request/url_request_netlog_params.h"
@@ -131,6 +132,9 @@ URLRequest::URLRequest(const GURL& url, Delegate* delegate)
 }
 
 URLRequest::~URLRequest() {
+  if (before_request_callback_)
+    before_request_callback_->Cancel();
+
   Cancel();
 
   if (job_)
@@ -354,6 +358,19 @@ GURL URLRequest::GetSanitizedReferrer() const {
 }
 
 void URLRequest::Start() {
+  response_info_.request_time = Time::Now();
+
+  if (context_ && context_->network_delegate()) {
+    before_request_callback_ = new CancelableCompletionCallback<URLRequest>(
+      this, &URLRequest::BeforeRequestComplete);
+    before_request_callback_->AddRef();  // balanced in BeforeRequestComplete
+    if (context_->network_delegate()->NotifyBeforeURLRequest(
+        this, before_request_callback_)) {
+      net_log_.BeginEvent(NetLog::TYPE_URL_REQUEST_BLOCKED_ON_EXTENSION, NULL);
+      return;  // paused
+    }
+  }
+
   StartJob(URLRequestJobManager::GetInstance()->CreateJob(this));
 }
 
@@ -363,11 +380,6 @@ void URLRequest::StartJob(URLRequestJob* job) {
   DCHECK(!is_pending_);
   DCHECK(!job_);
 
-  // TODO(mpcomplete): pass in request ID?
-  // TODO(mpcomplete): allow delegate to potentially delay/cancel request.
-  if (context_ && context_->network_delegate())
-    context_->network_delegate()->NotifyBeforeURLRequest(this);
-
   net_log_.BeginEvent(
       net::NetLog::TYPE_URL_REQUEST_START_JOB,
       make_scoped_refptr(new URLRequestStartEventParameters(
@@ -381,7 +393,6 @@ void URLRequest::StartJob(URLRequestJob* job) {
 
   is_pending_ = true;
 
-  response_info_.request_time = Time::Now();
   response_info_.was_cached = false;
 
   // Don't allow errors to be sent from within Start().
@@ -391,6 +402,18 @@ void URLRequest::StartJob(URLRequestJob* job) {
   job_->Start();
 }
 
+void URLRequest::BeforeRequestComplete(int error) {
+  DCHECK(!job_);
+
+  net_log_.EndEvent(NetLog::TYPE_URL_REQUEST_BLOCKED_ON_EXTENSION, NULL);
+  before_request_callback_->Release();  // balanced in Start
+  if (error != net::OK) {
+    StartJob(new URLRequestErrorJob(this, error));
+  } else {
+    StartJob(URLRequestJobManager::GetInstance()->CreateJob(this));
+  }
+}
+
 void URLRequest::Restart() {
   // Should only be called if the original job didn't make any progress.
   DCHECK(job_ && !job_->has_response_started());
@@ -539,6 +562,7 @@ void URLRequest::PrepareToRestart() {
   OrphanJob();
 
   response_info_ = net::HttpResponseInfo();
+  response_info_.request_time = Time::Now();
   status_ = URLRequestStatus();
   is_pending_ = false;
 }
diff --git a/net/url_request/url_request.h b/net/url_request/url_request.h
index 849a03b..72ab4d1 100644
--- a/net/url_request/url_request.h
+++ b/net/url_request/url_request.h
@@ -17,6 +17,7 @@
 #include "base/string16.h"
 #include "base/threading/non_thread_safe.h"
 #include "googleurl/src/gurl.h"
+#include "net/base/completion_callback.h"
 #include "net/base/load_states.h"
 #include "net/base/net_log.h"
 #include "net/base/request_priority.h"
@@ -607,6 +608,13 @@ class URLRequest : public base::NonThreadSafe {
   // passed values.
   void DoCancel(int os_error, const net::SSLInfo& ssl_info);
 
+  // Resumes or blocks a request paused by the NetworkDelegate::OnBeforeRequest
+  // handler. If |blocked| is true, the request is blocked and an error page is
+  // returned indicating so. This should only be called after Start is called
+  // and OnBeforeRequest returns true (signalling that the request should be
+  // paused).
+  void BeforeRequestComplete(int error);
+
   // Contextual information used for this request (can be NULL). This contains
   // most of the dependencies which are shared between requests (disk cache,
   // cookie store, socket pool, etc.)
@@ -664,6 +672,11 @@ class URLRequest : public base::NonThreadSafe {
 
   base::debug::LeakTracker<URLRequest> leak_tracker_;
 
+  // Callback passed to the network delegate to notify us when a blocked request
+  // is ready to be resumed or canceled.
+  scoped_refptr< CancelableCompletionCallback<URLRequest> >
+      before_request_callback_;
+
   DISALLOW_COPY_AND_ASSIGN(URLRequest);
 };
 
diff --git a/net/url_request/url_request_test_util.cc b/net/url_request/url_request_test_util.cc
index 5e76729..8fd7cab 100644
--- a/net/url_request/url_request_test_util.cc
+++ b/net/url_request/url_request_test_util.cc
@@ -296,7 +296,9 @@ TestNetworkDelegate::TestNetworkDelegate()
 
 TestNetworkDelegate::~TestNetworkDelegate() {}
 
-void TestNetworkDelegate::OnBeforeURLRequest(net::URLRequest* request) {
+bool TestNetworkDelegate::OnBeforeURLRequest(
+    net::URLRequest* request, net::CompletionCallback* callback) {
+  return false;
 }
 
 void TestNetworkDelegate::OnSendHttpRequest(
diff --git a/net/url_request/url_request_test_util.h b/net/url_request/url_request_test_util.h
index 47ecff4..d166f9e 100644
--- a/net/url_request/url_request_test_util.h
+++ b/net/url_request/url_request_test_util.h
@@ -201,7 +201,8 @@ class TestNetworkDelegate : public net::NetworkDelegate {
 
  private:
   // net::NetworkDelegate:
-  virtual void OnBeforeURLRequest(net::URLRequest* request);
+  virtual bool OnBeforeURLRequest(net::URLRequest* request,
+                                  net::CompletionCallback* callback);
   virtual void OnSendHttpRequest(net::HttpRequestHeaders* headers);
   virtual void OnResponseStarted(net::URLRequest* request);
   virtual void OnReadCompleted(net::URLRequest* request, int bytes_read);
diff --git a/third_party/skia/LICENSE b/third_party/skia/LICENSE
deleted file mode 100644
index d645695..0000000
--- a/third_party/skia/LICENSE
+++ /dev/null
@@ -1,202 +0,0 @@
-
-                                 Apache License
-                           Version 2.0, January 2004
-                        http://www.apache.org/licenses/
-
-   TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
-
-   1. Definitions.
-
-      "License" shall mean the terms and conditions for use, reproduction,
-      and distribution as defined by Sections 1 through 9 of this document.
-
-      "Licensor" shall mean the copyright owner or entity authorized by
-      the copyright owner that is granting the License.
-
-      "Legal Entity" shall mean the union of the acting entity and all
-      other entities that control, are controlled by, or are under common
-      control with that entity. For the purposes of this definition,
-      "control" means (i) the power, direct or indirect, to cause the
-      direction or management of such entity, whether by contract or
-      otherwise, or (ii) ownership of fifty percent (50%) or more of the
-      outstanding shares, or (iii) beneficial ownership of such entity.
-
-      "You" (or "Your") shall mean an individual or Legal Entity
-      exercising permissions granted by this License.
-
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diff --git a/third_party/skia/README.chromium b/third_party/skia/README.chromium
deleted file mode 100644
index ea65a69..0000000
--- a/third_party/skia/README.chromium
+++ /dev/null
@@ -1,2 +0,0 @@
-Name: skia
-URL: http://code.google.com/p/skia