Move Task Scheduler Initialization From ios/chrome/browser to Web

ios/chrome/browser/ios_chrome_main_parts.mm

 // Copyright 2016 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 "ios/chrome/browser/ios_chrome_main_parts.h"
 
 #include "base/base_switches.h"
 #include "base/feature_list.h"
 #include "base/files/file_path.h"
 #include "base/logging.h"
 #include "base/memory/ptr_util.h"
 #include "base/metrics/user_metrics.h"
 #include "base/path_service.h"
-#include "base/task_scheduler/task_scheduler.h"
 #include "base/time/default_tick_clock.h"
 #include "components/content_settings/core/browser/cookie_settings.h"
 #include "components/content_settings/core/common/content_settings_pattern.h"
 #include "components/flags_ui/pref_service_flags_storage.h"
 #include "components/language_usage_metrics/language_usage_metrics.h"
 #include "components/metrics/metrics_service.h"
 #include "components/metrics/profiler/ios/ios_tracking_synchronizer_delegate.h"
 #include "components/metrics/profiler/tracking_synchronizer.h"
 #include "components/metrics_services_manager/metrics_services_manager.h"
 #include "components/open_from_clipboard/clipboard_recent_content.h"
 #include "components/prefs/json_pref_store.h"
 #include "components/prefs/pref_service.h"
 #include "components/rappor/rappor_service_impl.h"
-#include "components/task_scheduler_util/initialization_util.h"
 #include "components/translate/core/browser/translate_download_manager.h"
 #include "components/variations/field_trial_config/field_trial_util.h"
 #include "components/variations/service/variations_service.h"
 #include "components/variations/variations_http_header_provider.h"
 #include "components/variations/variations_switches.h"
 #include "ios/chrome/browser/about_flags.h"
 #include "ios/chrome/browser/application_context_impl.h"
 #include "ios/chrome/browser/browser_state/browser_state_keyed_service_factories.h"
 #include "ios/chrome/browser/browser_state/chrome_browser_state.h"
 #include "ios/chrome/browser/browser_state/chrome_browser_state_manager.h"
@@ skipping 43 matching lines @@
           std::string(), nullptr, ResourceBundle::LOAD_COMMON_RESOURCES);
   CHECK(!loaded_locale.empty());
 
   base::FilePath resources_pack_path;
   PathService::Get(ios::FILE_RESOURCES_PACK, &resources_pack_path);
   ResourceBundle::GetSharedInstance().AddDataPackFromPath(
       resources_pack_path, ui::SCALE_FACTOR_100P);
 }
 
 void IOSChromeMainParts::PreCreateThreads() {
+  // IMPORTANT
+  // Calls in this function should not post tasks or create threads as
+  // components used to handle those tasks are not yet available. This work
+  // should be deferred to PreMainMessageLoopRunImpl.
+
   base::FilePath local_state_path;
   CHECK(PathService::Get(ios::FILE_LOCAL_STATE, &local_state_path));
   scoped_refptr<base::SequencedTaskRunner> local_state_task_runner =
       JsonPrefStore::GetTaskRunnerForFile(local_state_path,
                                           web::WebThread::GetBlockingPool());
   application_context_.reset(new ApplicationContextImpl(
       local_state_task_runner.get(), parsed_command_line_,
       l10n_util::GetLocaleOverride()));
   DCHECK_EQ(application_context_.get(), GetApplicationContext());
 
@@ skipping 10 matching lines @@
   flags_ui::PrefServiceFlagsStorage flags_storage(
       application_context_->GetLocalState());
   ConvertFlagsToSwitches(&flags_storage,
                          base::CommandLine::ForCurrentProcess());
 
   // Initialize tracking synchronizer system.
   tracking_synchronizer_ = new metrics::TrackingSynchronizer(
       base::MakeUnique<base::DefaultTickClock>(),
       base::Bind(&metrics::IOSTrackingSynchronizerDelegate::Create));
 
-  // IMPORTANT
-  // Do not add anything below this line until you've verified your new code
-  // does not interfere with the critical initialization order below. Some of
-  // the calls below end up implicitly creating threads and as such new calls
-  // typically either belong before them or in a later startup phase.
-
   // Now that the command line has been mutated based on about:flags, we can
-  // initialize field trials and setup metrics. The field trials are needed by
-  // IOThread's initialization in ApplicationContext's PreCreateThreads.
+  // initialize field trials. The field trials are needed by IOThread's
+  // initialization which happens in BrowserProcess:PreCreateThreads. Metrics
+  // initialization is handled in PreMainMessageLoopRun since it posts tasks.
   SetupFieldTrials();
 
-  // Task Scheduler initialization needs to be here for the following reasons:
-  //   * After |SetupFieldTrials()|: Initialization uses variations.
-  //   * Near the end of |PreCreateThreads()|: The TaskScheduler needs to be
-  //         created before any other threads are (by contract) but it creates
-  //         threads itself so instantiating it earlier is also incorrect.
-  // To maintain scoping symmetry, if this line is moved, the corresponding
-  // shutdown call may also need to be moved.
-  task_scheduler_util::InitializeDefaultBrowserTaskScheduler();
-
-
   // Initialize FieldTrialSynchronizer system.
   field_trial_synchronizer_.reset(new ios::FieldTrialSynchronizer);
 
   application_context_->PreCreateThreads();
 }
 
 void IOSChromeMainParts::PreMainMessageLoopRun() {
   // This must occur at PreMainMessageLoopRun because |SetupMetrics()| uses the
   // blocking pool, which is disabled until the CreateThreads phase of startup.
   SetupMetrics();
@@ skipping 56 matching lines @@
       last_used_browser_state->GetPrefs());
 }
 
 void IOSChromeMainParts::PostMainMessageLoopRun() {
   TranslateServiceIOS::Shutdown();
   application_context_->StartTearDown();
 }
 
 void IOSChromeMainParts::PostDestroyThreads() {
   application_context_->PostDestroyThreads();
-
-  // The TaskScheduler was initialized before invoking
-  // |application_context_->PreCreateThreads()|. To maintain scoping symmetry,
-  // perform the shutdown after |application_context_->PostDestroyThreads()|.
-  base::TaskScheduler* task_scheduler = base::TaskScheduler::GetInstance();
-  if (task_scheduler)
-    task_scheduler->Shutdown();
 }
 
 // This will be called after the command-line has been mutated by about:flags
 void IOSChromeMainParts::SetupFieldTrials() {
   base::SetRecordActionTaskRunner(
       web::WebThread::GetTaskRunnerForThread(web::WebThread::UI));
 
   // Initialize FieldTrialList to support FieldTrials that use one-time
   // randomization.
   DCHECK(!field_trial_list_);
@@ skipping 66 matching lines @@
 
 void IOSChromeMainParts::StartMetricsRecording() {
   bool wifiOnly = local_state_->GetBoolean(prefs::kMetricsReportingWifiOnly);
   bool isConnectionCellular = net::NetworkChangeNotifier::IsConnectionCellular(
       net::NetworkChangeNotifier::GetConnectionType());
   bool mayUpload = !wifiOnly || !isConnectionCellular;
 
   application_context_->GetMetricsServicesManager()->UpdateUploadPermissions(
       mayUpload);
 }