This defers starting background extension page RenderViews

chrome/browser/profiles/profile_manager.cc

 // 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/profiles/profile_manager.h"
 
 #include <set>
 
 #include "base/bind.h"
 #include "base/command_line.h"
 #include "base/debug/trace_event.h"
 #include "base/deferred_sequenced_task_runner.h"
 #include "base/file_util.h"
 #include "base/files/file_enumerator.h"
 #include "base/files/file_path.h"
+#include "base/metrics/field_trial.h"
 #include "base/metrics/histogram.h"
 #include "base/prefs/pref_service.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
 #include "chrome/browser/bookmarks/bookmark_model.h"
 #include "chrome/browser/bookmarks/bookmark_model_factory.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/chrome_notification_types.h"
 #include "chrome/browser/content_settings/host_content_settings_map.h"
@@ skipping 700 matching lines @@
   ProfileMetrics::LogNumberOfProfiles(this);
   content::NotificationService::current()->Notify(
       chrome::NOTIFICATION_PROFILE_ADDED,
       content::Source<Profile>(profile),
       content::NotificationService::NoDetails());
 }
 
 void ProfileManager::DoFinalInitForServices(Profile* profile,
                                             bool go_off_the_record) {
 #if defined(ENABLE_EXTENSIONS)
+  // Set up a field trial to determine the effectiveness of deferring
+  // creation of background extension RenderViews.
+  CR_DEFINE_STATIC_LOCAL(scoped_refptr<base::FieldTrial>, trial, ());
+  static bool defer_creation = false;
+
+  if (!trial.get()) {
+    const base::FieldTrial::Probability kDivisor = 100;
+
+    // Enable the deferred creation for 50% of the users.
+    base::FieldTrial::Probability probability_per_group = 50;
+
+    // After August 31, 2014 builds, it will always be in default group
+    // (defer_creation == false).
+    trial = base::FieldTrialList::FactoryGetFieldTrial(
+        "DeferBackgroundExtensionCreation",
+        kDivisor,
+        "RateLimited",
+        2014,
+        8,
+        31,
+        base::FieldTrial::ONE_TIME_RANDOMIZED,
+        NULL);
+
+    // Add group for deferred creation of background extension RenderViews.
+    int defer_creation_group =
+        trial->AppendGroup("Deferred", probability_per_group);
+    defer_creation = trial->group() == defer_creation_group;
+  }
+
   extensions::ExtensionSystem::Get(profile)->InitForRegularProfile(
-      !go_off_the_record);
+      !go_off_the_record, defer_creation);
   // During tests, when |profile| is an instance of TestingProfile,
   // ExtensionSystem might not create an ExtensionService.
   if (extensions::ExtensionSystem::Get(profile)->extension_service()) {
     profile->GetHostContentSettingsMap()->RegisterExtensionService(
         extensions::ExtensionSystem::Get(profile)->extension_service());
   }
 #endif
 #if defined(ENABLE_MANAGED_USERS)
   // Initialization needs to happen after extension system initialization (for
   // extension::ManagementPolicy) and InitProfileUserPrefs (for setting the
@@ skipping 394 matching lines @@
 ProfileManager::ProfileInfo::ProfileInfo(
     Profile* profile,
     bool created)
     : profile(profile),
       created(created) {
 }
 
 ProfileManager::ProfileInfo::~ProfileInfo() {
   ProfileDestroyer::DestroyProfileWhenAppropriate(profile.release());
 }