Move Task Scheduler Initialization From chrome/browser to Content

chrome/browser/chrome_browser_main.cc

Index: chrome/browser/chrome_browser_main.cc
diff --git a/chrome/browser/chrome_browser_main.cc b/chrome/browser/chrome_browser_main.cc
index a9aaea8c7d26e8797aedf057dbfe6840c3fa8128..53ab0687c8ef5622340dae2455744bf0cb7ed342 100644
--- a/chrome/browser/chrome_browser_main.cc
+++ b/chrome/browser/chrome_browser_main.cc
@@ -33,7 +33,6 @@
 #include "base/strings/sys_string_conversions.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/sys_info.h"
-#include "base/task_scheduler/task_scheduler.h"
 #include "base/threading/platform_thread.h"
 #include "base/time/default_tick_clock.h"
 #include "base/time/time.h"
@@ -135,7 +134,6 @@
 #include "components/rappor/rappor_service.h"
 #include "components/signin/core/common/profile_management_switches.h"
 #include "components/startup_metric_utils/browser/startup_metric_utils.h"
-#include "components/task_scheduler_util/initialization_util.h"
 #include "components/tracing/common/tracing_switches.h"
 #include "components/translate/core/browser/translate_download_manager.h"
 #include "components/variations/field_trial_config/field_trial_util.h"
@@ -1201,24 +1199,15 @@ int ChromeBrowserMainParts::PreCreateThreadsImpl() {
 
   // IMPORTANT

[gab, 2016/11/30 22:36:58]

Does this comment apply anymore? i.e. it's relevant to this whole method but the
things at the end here are no longer special?

[robliao, 2016/12/06 01:31:30]

Moved to top and reworded.

   // 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.
+  // does not interfere with the critical initialization order below. Calls
+  // after this line should not post tasks or create threads. This work should
+  // be deferred to PreMainMessageLoopRunImpl.
 
   // 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

[gab, 2016/11/30 22:36:58]

No longer sets up metrics

[robliao, 2016/12/06 01:31:30]

Reworded. The only implication here is that we can now setup metrics but we wait
for PreMainMessageLoopRunImpl.

   // IOThread's initialization which happens in BrowserProcess:PreCreateThreads.
   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();
-
   // ChromeOS needs ResourceBundle::InitSharedInstance to be called before this.
   // This also instantiates the IOThread which requests the metrics service and
   // must be after |SetupMetrics()|.
@@ -2070,13 +2059,6 @@ void ChromeBrowserMainParts::PostDestroyThreads() {
   // release it.
   ignore_result(browser_process_.release());
 
-  // The TaskScheduler was initialized before invoking
-  // |browser_process_->PreCreateThreads()|. To maintain scoping symmetry,
-  // perform the shutdown after |browser_process_->PostDestroyThreads()|.
-  base::TaskScheduler* task_scheduler = base::TaskScheduler::GetInstance();
-  if (task_scheduler)
-    task_scheduler->Shutdown();
-
   browser_shutdown::ShutdownPostThreadsStop(restart_flags);
   master_prefs_.reset();
   process_singleton_.reset();