Add an experiment to redirect SequencedWorkerPool tasks to TaskScheduler.

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 <algorithm>
@@ skipping 23 matching lines @@
 #include "base/strings/string_piece.h"
 #include "base/strings/string_split.h"
 #include "base/strings/sys_string_conversions.h"
 #include "base/strings/utf_string_conversions.h"
 #include "base/sys_info.h"
 #include "base/task_scheduler/scheduler_worker_pool_params.h"
 #include "base/task_scheduler/switches.h"
 #include "base/task_scheduler/task_scheduler.h"
 #include "base/task_scheduler/task_traits.h"
 #include "base/threading/platform_thread.h"
+#include "base/threading/sequenced_worker_pool.h"
 #include "base/time/default_tick_clock.h"
 #include "base/time/time.h"
 #include "base/trace_event/trace_event.h"
 #include "base/values.h"
 #include "build/build_config.h"
 #include "cc/base/switches.h"
 #include "chrome/browser/about_flags.h"
 #include "chrome/browser/after_startup_task_utils.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/browser_process_impl.h"
@@ skipping 391 matching lines @@
                                predefined_params.priority_hint,
                                predefined_params.io_restriction,
                                variation_values.threads,
                                variation_values.detach_period);
   }
 
   DCHECK_EQ(WORKER_POOL_COUNT, params_vector.size());
 
   base::TaskScheduler::CreateAndSetDefaultTaskScheduler(
       params_vector, base::Bind(WorkerPoolIndexForTraits));
+
+  // TODO(gab): Remove this when http://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::
+        RedirectSequencedWorkerPoolsToTaskSchedulerForProcess();
+  }
 }
 
 // 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 875 matching lines @@
   chromeos::CrosSettings::Initialize();
 #endif  // defined(OS_CHROMEOS)
 
   SetupOriginTrialsCommandLine();
 
   // Now the command line has been mutated based on about:flags, we can setup
   // metrics and initialize field trials. The field trials are needed by
   // IOThread's initialization which happens in BrowserProcess:PreCreateThreads.
   SetupMetricsAndFieldTrials();
 
-  MaybeInitializeTaskScheduler();
-
   // ChromeOS needs ResourceBundle::InitSharedInstance to be called before this.
   browser_process_->PreCreateThreads();
 
   device::GeolocationProvider::SetGeolocationDelegate(
       new ChromeGeolocationDelegate());
 
+  // This needs to be the last thing in PreCreateThreads() because 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. It also has to be after SetupMetricsAndFieldTrials() to allow it
+  // to use field trials. Note: it could also be the first thing in
+  // CreateThreads() but being in chrome/ is convenient for now as the
+  // initialization uses variations parameters extensively.
+  MaybeInitializeTaskScheduler();
+
   return content::RESULT_CODE_NORMAL_EXIT;
 }
 
 void ChromeBrowserMainParts::MojoShellConnectionStarted(
     content::MojoShellConnection* connection) {
   for (size_t i = 0; i < chrome_extra_parts_.size(); ++i)
     chrome_extra_parts_[i]->MojoShellConnectionStarted(connection);
 }
 
 void ChromeBrowserMainParts::PreMainMessageLoopRun() {
@@ skipping 841 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);
 }