Use the "DNS prefetch" button to control whether prerender is enabled/disabled.

This also removes prerender from about:flags.

BUG=77783
TEST=Force prerender on [via --prerender=enabled] and toggle the checkbox on/off to dynamically adjust prerender.

Review URL: http://codereview.chromium.org/6771018

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@79986 0039d316-1c4b-4281-b951-d872f2087c98

10 files changed, 54 insertions, 40 deletions

diff --git a/chrome/app/generated_resources.grd b/chrome/app/generated_resources.grd
index 619fb0b2..895fa51 100644
--- a/chrome/app/generated_resources.grd
+++ b/chrome/app/generated_resources.grd
@@ -4131,21 +4131,6 @@ Keep your key file in a safe place. You will need it to create new versions of y
       <message name="IDS_FLAGS_DNS_SERVER_DESCRIPTION" desc="">
         User specified DNS server, which Chrome will use for DNS resolutions rather than the system defaults.
       </message>
-      <message name="IDS_FLAGS_PAGE_PRERENDER_NAME" desc="Name of the 'Prerendering' lab.">
-        Web Page Prerendering.
-      </message>
-      <message name="IDS_FLAGS_PAGE_PRERENDER_DESCRIPTION" desc="Description of the 'Prerendering' lab.">
-        Speculatively prerenders complete webpages in the background for a faster browsing experience.  The default setting of automatic can cause this feature to enable/disable randomly for testing purposes.\n
-      </message>
-      <message name="IDS_FLAGS_PAGE_PRERENDER_AUTOMATIC" desc="Option name for automatic selection in the 'Prerendering' lab">
-	Automatic
-      </message>
-      <message name="IDS_FLAGS_PAGE_PRERENDER_ENABLED" desc="Option name for always enabling the 'Prerendering' lab">
-	Always Enabled
-      </message>
-      <message name="IDS_FLAGS_PAGE_PRERENDER_DISABLED" desc="Option name for always disabling the 'Prerendering' lab">
-	Always Disabled
-      </message>
       <message name="IDS_FLAGS_EXPERIMENTAL_EXTENSION_APIS_NAME" desc="Name of the 'Experimental Extension APIs' lab.">
         Experimental Extension APIs
       </message>
diff --git a/chrome/browser/about_flags.cc b/chrome/browser/about_flags.cc
index d251cba..d48ae0c 100644
--- a/chrome/browser/about_flags.cc
+++ b/chrome/browser/about_flags.cc
@@ -41,14 +41,6 @@ const char kMediaPlayerExperimentName[] = "media-player";
 const char kAdvancedFileSystemExperimentName[] = "advanced-file-system";
 const char kVerticalTabsExperimentName[] = "vertical-tabs";
 
-const Experiment::Choice kPagePrerenderChoices[] = {
-  { IDS_FLAGS_PAGE_PRERENDER_AUTOMATIC, "", "" },
-  { IDS_FLAGS_PAGE_PRERENDER_ENABLED,
-    switches::kPrerender, switches::kPrerenderSwitchValueEnabled },
-  { IDS_FLAGS_PAGE_PRERENDER_DISABLED,
-    switches::kPrerender, switches::kPrerenderSwitchValueDisabled },
-};
-
 // RECORDING USER METRICS FOR FLAGS:
 // -----------------------------------------------------------------------------
 // The first line of the experiment is the internal name. If you'd like to
@@ -213,13 +205,6 @@ const Experiment kExperiments[] = {
     SINGLE_VALUE_TYPE(switches::kDnsServer)
   },
   {
-    "page-prerender",  // FLAGS:RECORD_UMA
-    IDS_FLAGS_PAGE_PRERENDER_NAME,
-    IDS_FLAGS_PAGE_PRERENDER_DESCRIPTION,
-    kOsAll,
-    MULTI_VALUE_TYPE(kPagePrerenderChoices)
-  },
-  {
     "extension-apis",  // FLAGS:RECORD_UMA
     IDS_FLAGS_EXPERIMENTAL_EXTENSION_APIS_NAME,
     IDS_FLAGS_EXPERIMENTAL_EXTENSION_APIS_DESCRIPTION,
diff --git a/chrome/browser/net/net_pref_observer.cc b/chrome/browser/net/net_pref_observer.cc
index 75dd11a..0a1a01c 100644
--- a/chrome/browser/net/net_pref_observer.cc
+++ b/chrome/browser/net/net_pref_observer.cc
@@ -7,6 +7,8 @@
 #include "base/task.h"
 #include "chrome/browser/net/predictor_api.h"
 #include "chrome/browser/prefs/pref_service.h"
+#include "chrome/browser/prerender/prerender_manager.h"
+#include "chrome/browser/profiles/profile.h"
 #include "chrome/common/pref_names.h"
 #include "content/browser/browser_thread.h"
 #include "content/common/notification_type.h"
@@ -25,9 +27,11 @@ void SetEnforceThrottlingOnThrottlerManager(bool enforce) {
 
 }
 
-NetPrefObserver::NetPrefObserver(PrefService* prefs) {
+NetPrefObserver::NetPrefObserver(PrefService* prefs,
+                                 prerender::PrerenderManager* prerender_manager)
+    : prerender_manager_(prerender_manager) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
-
+  DCHECK(prefs);
   dns_prefetching_enabled_.Init(prefs::kDnsPrefetchingEnabled, prefs, this);
   spdy_disabled_.Init(prefs::kDisableSpdy, prefs, this);
   http_throttling_enabled_.Init(prefs::kHttpThrottlingEnabled, prefs, this);
@@ -52,6 +56,8 @@ void NetPrefObserver::ApplySettings(const std::string* pref_name) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
 
   chrome_browser_net::EnablePredictor(*dns_prefetching_enabled_);
+  if (prerender_manager_)
+    prerender_manager_->set_enabled(*dns_prefetching_enabled_);
   net::HttpStreamFactory::set_spdy_enabled(!*spdy_disabled_);
 
   if (!pref_name || *pref_name == prefs::kHttpThrottlingEnabled) {
diff --git a/chrome/browser/net/net_pref_observer.h b/chrome/browser/net/net_pref_observer.h
index a1fd2bd..3c33c16 100644
--- a/chrome/browser/net/net_pref_observer.h
+++ b/chrome/browser/net/net_pref_observer.h
@@ -12,12 +12,21 @@
 #include "chrome/browser/prefs/pref_member.h"
 #include "content/common/notification_observer.h"
 
+class Profile;
+
+namespace prerender {
+class PrerenderManager;
+}
+
 // Monitors network-related preferences for changes and applies them.
 // The supplied PrefService must outlive this NetPrefObserver.
 // Must be used only on the UI thread.
 class NetPrefObserver : public NotificationObserver {
  public:
-  explicit NetPrefObserver(PrefService* prefs);
+  // |prefs| must outlive this NetPrefObserver. A reference is
+  // held to |prerender_manager| if it is non-NULL.
+  NetPrefObserver(PrefService* prefs,
+                  prerender::PrerenderManager* prerender_manager);
   ~NetPrefObserver();
 
   // NotificationObserver
@@ -34,6 +43,7 @@ class NetPrefObserver : public NotificationObserver {
   BooleanPrefMember dns_prefetching_enabled_;
   BooleanPrefMember spdy_disabled_;
   BooleanPrefMember http_throttling_enabled_;
+  scoped_refptr<prerender::PrerenderManager> prerender_manager_;
 
   DISALLOW_COPY_AND_ASSIGN(NetPrefObserver);
 };
diff --git a/chrome/browser/prerender/prerender_manager.cc b/chrome/browser/prerender/prerender_manager.cc
index aa2eb01..2a6ee7c 100644
--- a/chrome/browser/prerender/prerender_manager.cc
+++ b/chrome/browser/prerender/prerender_manager.cc
@@ -44,7 +44,7 @@ void PrerenderManager::SetMode(PrerenderManagerMode mode) {
 }
 
 // static
-bool PrerenderManager::IsPrerenderingEnabled() {
+bool PrerenderManager::IsPrerenderingPossible() {
   return
       GetMode() == PRERENDER_MODE_ENABLED ||
       GetMode() == PRERENDER_MODE_EXPERIMENT_PRERENDER_GROUP ||
@@ -78,6 +78,7 @@ struct PrerenderManager::PendingContentsData {
 
 PrerenderManager::PrerenderManager(Profile* profile)
     : rate_limit_enabled_(true),
+      enabled_(true),
       profile_(profile),
       max_prerender_age_(base::TimeDelta::FromSeconds(
           kDefaultMaxPrerenderAgeSeconds)),
@@ -382,6 +383,16 @@ void PrerenderManager::RecordTimeUntilUsed(base::TimeDelta time_until_used) {
       50);
 }
 
+bool PrerenderManager::is_enabled() const {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  return enabled_;
+}
+
+void PrerenderManager::set_enabled(bool enabled) {
+  DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  enabled_ = enabled;
+}
+
 PrerenderContents* PrerenderManager::FindEntry(const GURL& url) {
   for (std::list<PrerenderContentsData>::iterator it = prerender_list_.begin();
        it != prerender_list_.end();
diff --git a/chrome/browser/prerender/prerender_manager.h b/chrome/browser/prerender/prerender_manager.h
index 81e2ccd..74dd2d3 100644
--- a/chrome/browser/prerender/prerender_manager.h
+++ b/chrome/browser/prerender/prerender_manager.h
@@ -97,9 +97,19 @@ class PrerenderManager : public base::RefCounted<PrerenderManager> {
   unsigned int max_elements() const { return max_elements_; }
   void set_max_elements(unsigned int num) { max_elements_ = num; }
 
+  // Returns whether prerendering is currently enabled for this manager.
+  // Must be called on the UI thread.
+  bool is_enabled() const;
+
+  // Set whether prerendering is currently enabled for this manager.
+  // Must be called on the UI thread.
+  // If |enabled| is false, existing prerendered pages will still persist until
+  // they time out, but new ones will not be generated.
+  void set_enabled(bool enabled);
+
   static PrerenderManagerMode GetMode();
   static void SetMode(PrerenderManagerMode mode);
-  static bool IsPrerenderingEnabled();
+  static bool IsPrerenderingPossible();
   static bool IsControlGroup();
 
   // The following static method can be called from any thread, but will result
@@ -166,6 +176,11 @@ class PrerenderManager : public base::RefCounted<PrerenderManager> {
 
   bool DoesRateLimitAllowPrerender() const;
 
+  // Specifies whether prerendering is currently enabled for this
+  // manager. The value can change dynamically during the lifetime
+  // of the PrerenderManager.
+  bool enabled_;
+
   Profile* profile_;
 
   base::TimeDelta max_prerender_age_;
diff --git a/chrome/browser/prerender/prerender_resource_handler.cc b/chrome/browser/prerender/prerender_resource_handler.cc
index f5567c7..0a7b507 100644
--- a/chrome/browser/prerender/prerender_resource_handler.cc
+++ b/chrome/browser/prerender/prerender_resource_handler.cc
@@ -202,6 +202,8 @@ void PrerenderResourceHandler::StartPrerender(
     const GURL& referrer,
     bool make_pending) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::UI));
+  if (!prerender_manager_->is_enabled())
+    return;
   if (make_pending) {
     prerender_manager_->AddPendingPreload(child_route_id_pair,
                                           url, alias_urls, referrer);
diff --git a/chrome/browser/profiles/profile_impl.cc b/chrome/browser/profiles/profile_impl.cc
index 5b60dc8..ff46694 100644
--- a/chrome/browser/profiles/profile_impl.cc
+++ b/chrome/browser/profiles/profile_impl.cc
@@ -771,7 +771,8 @@ PrefService* ProfileImpl::GetPrefs() {
         GetExtensionPrefValueMap()));
 
     DCHECK(!net_pref_observer_.get());
-    net_pref_observer_.reset(new NetPrefObserver(prefs_.get()));
+    net_pref_observer_.reset(
+        new NetPrefObserver(prefs_.get(), GetPrerenderManager()));
   }
 
   return prefs_.get();
@@ -1492,7 +1493,7 @@ PrefProxyConfigTracker* ProfileImpl::GetProxyConfigTracker() {
 }
 
 prerender::PrerenderManager* ProfileImpl::GetPrerenderManager() {
-  if (!prerender::PrerenderManager::IsPrerenderingEnabled())
+  if (!prerender::PrerenderManager::IsPrerenderingPossible())
     return NULL;
   if (!prerender_manager_)
     prerender_manager_ = new prerender::PrerenderManager(this);
diff --git a/chrome/browser/profiles/profile_impl.h b/chrome/browser/profiles/profile_impl.h
index 73f403b..ffc3fe8 100644
--- a/chrome/browser/profiles/profile_impl.h
+++ b/chrome/browser/profiles/profile_impl.h
@@ -208,6 +208,7 @@ class ProfileImpl : public Profile,
   scoped_refptr<TransportSecurityPersister>
       transport_security_persister_;
   scoped_ptr<policy::ProfilePolicyConnector> profile_policy_connector_;
+  scoped_refptr<prerender::PrerenderManager> prerender_manager_;
   scoped_ptr<NetPrefObserver> net_pref_observer_;
   scoped_ptr<TemplateURLFetcher> template_url_fetcher_;
   scoped_ptr<TemplateURLModel> template_url_model_;
@@ -307,8 +308,6 @@ class ProfileImpl : public Profile,
 
   scoped_refptr<PrefProxyConfigTracker> pref_proxy_config_tracker_;
 
-  scoped_refptr<prerender::PrerenderManager> prerender_manager_;
-
   scoped_ptr<ChromeURLDataManager> chrome_url_data_manager_;
 
   DISALLOW_COPY_AND_ASSIGN(ProfileImpl);
diff --git a/chrome/test/testing_profile.cc b/chrome/test/testing_profile.cc
index a2b9a0f..9d32203 100644
--- a/chrome/test/testing_profile.cc
+++ b/chrome/test/testing_profile.cc
@@ -770,7 +770,7 @@ ChromeURLDataManager* TestingProfile::GetChromeURLDataManager() {
 }
 
 prerender::PrerenderManager* TestingProfile::GetPrerenderManager() {
-  if (!prerender::PrerenderManager::IsPrerenderingEnabled())
+  if (!prerender::PrerenderManager::IsPrerenderingPossible())
     return NULL;
   if (!prerender_manager_)
     prerender_manager_ = new prerender::PrerenderManager(this);