Redirect HistoryService thread to TaskScheduler via a field trial.

chrome/browser/chrome_browser_main.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/chrome_browser_main.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <map>
@@ skipping 104 matching lines @@
 #include "chrome/common/net/net_resource_provider.h"
 #include "chrome/common/pref_names.h"
 #include "chrome/common/profiling.h"
 #include "chrome/common/stack_sampling_configuration.h"
 #include "chrome/grit/generated_resources.h"
 #include "chrome/installer/util/google_update_settings.h"
 #include "components/component_updater/component_updater_service.h"
 #include "components/device_event_log/device_event_log.h"
 #include "components/flags_ui/pref_service_flags_storage.h"
 #include "components/google/core/browser/google_util.h"
+#include "components/history/core/browser/history_service.h"
 #include "components/language_usage_metrics/language_usage_metrics.h"
 #include "components/metrics/call_stack_profile_metrics_provider.h"
 #include "components/metrics/metrics_reporting_default_state.h"
 #include "components/metrics/metrics_service.h"
 #include "components/metrics/profiler/content/content_tracking_synchronizer_delegate.h"
 #include "components/metrics/profiler/tracking_synchronizer.h"
 #include "components/metrics_services_manager/metrics_services_manager.h"
 #include "components/nacl/browser/nacl_browser.h"
 #include "components/prefs/json_pref_store.h"
 #include "components/prefs/pref_registry_simple.h"
@@ skipping 188 matching lines @@
         << "The Browser Task Scheduler remains disabled with "
         << switches::kEnableBrowserTaskScheduler
         << " because there is no available variation param for this build or "
            " the task scheduler is disabled in chrome://flags.";
     return;
   }
 
   if (!task_scheduler_util::InitializeDefaultTaskScheduler(variation_params))
     return;
 
-  // TODO(gab): Remove this when http://crbug.com/622400 concludes.
+  // TODO(gab): Remove this when https://crbug.com/622400 concludes.
   const auto sequenced_worker_pool_param =
       variation_params.find("RedirectSequencedWorkerPools");
   if (sequenced_worker_pool_param != variation_params.end() &&
       sequenced_worker_pool_param->second == "true") {
     base::SequencedWorkerPool::RedirectToTaskSchedulerForProcess();
   }
+
+  // TODO(fdoray): Remove this when https://crbug.com/661143 concludes.

[robliao, 2016/11/08 22:21:50]

Add this to ios_chrome_main_parts.mm.

Side thought, can be done in a separate CL: Might be a good idea to centralize
the redirection portion in components/task_scheduler_utils.

+  const auto history_service_param =
+      variation_params.find("RedirectHistoryService");
+  if (history_service_param != variation_params.end() &&
+      history_service_param->second == "true") {
+    history::HistoryService::RedirectToTaskSchedulerForProcess();
+  }
 }
 
 // Returns the new local state object, guaranteed non-NULL.
 // |local_state_task_runner| must be a shutdown-blocking task runner.
 PrefService* InitializeLocalState(
     base::SequencedTaskRunner* local_state_task_runner,
     const base::CommandLine& parsed_command_line) {
   TRACE_EVENT0("startup", "ChromeBrowserMainParts::InitializeLocalState")
 
   // Load local state.  This includes the application locale so we know which
@@ skipping 1765 matching lines @@
   chromeos::CrosSettings::Shutdown();
 #endif  // defined(OS_CHROMEOS)
 #endif  // defined(OS_ANDROID)
 }
 
 // Public members:
 
 void ChromeBrowserMainParts::AddParts(ChromeBrowserMainExtraParts* parts) {
   chrome_extra_parts_.push_back(parts);
 }