Create TaskScheduler in BrowserMainLoop constructor.

content/browser/browser_main_loop.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 "content/browser/browser_main_loop.h"
 
 #include <stddef.h>
 
 #include <string>
 #include <utility>
@@ skipping 514 matching lines @@
       result_code_(RESULT_CODE_NORMAL_EXIT),
       created_threads_(false),
       // ContentMainRunner should have enabled tracing of the browser process
       // when kTraceStartup or kTraceConfigFile is in the command line.
       is_tracing_startup_for_duration_(
           parameters.command_line.HasSwitch(switches::kTraceStartup) ||
           (tracing::TraceConfigFile::GetInstance()->IsEnabled() &&
            tracing::TraceConfigFile::GetInstance()->GetStartupDuration() > 0)) {
   DCHECK(!g_current_browser_main_loop);
   g_current_browser_main_loop = this;
+
+  base::TaskScheduler::Create("");

[robliao, 2017/04/24 18:15:54]

Should we be more aggressive about the creation point now? Maybe
browser_main_runner is the place to be?

[gab, 2017/04/25 15:29:15]

Agreed for ASAP but this is essentially the same logical point: BrowserMainLoop
is called from BrowserMainRunnerImpl::Initialize() and BrowserMain() invokes
BrowserMainRunner::Create() and BrowserMainRunnerImpl::Initialize() in a row @
https://cs.chromium.org/chromium/src/content/browser/browser_main.cc?rcl=76b4...

So since this boils down to pretty much as early as possible in both cases, I'd
say here is better since it's what manages threads and pools.

[robliao, 2017/04/25 17:21:30]

I think this change is fine for now, but given that we will be removing the
browser threads management portion long term, it may make more sense to abstract
that outside of BrowserMainLoop when we arrive at that point.

 }
 

[robliao, 2017/04/25 17:21:30]

Document the use of "".

 BrowserMainLoop::~BrowserMainLoop() {
   DCHECK_EQ(this, g_current_browser_main_loop);
   ui::Clipboard::DestroyClipboardForCurrentThread();
   g_current_browser_main_loop = NULL;
 }
 
 void BrowserMainLoop::Init() {
   TRACE_EVENT0("startup", "BrowserMainLoop::Init");
 
   parts_.reset(
@@ skipping 398 matching lines @@
     startup_task_runner_->RunAllTasksNow();
   }
 #else
   startup_task_runner_->RunAllTasksNow();
 #endif
 }
 
 int BrowserMainLoop::CreateThreads() {
   TRACE_EVENT0("startup,rail", "BrowserMainLoop::CreateThreads");
 
-  auto task_scheduler_init_params =
-      GetContentClient()->browser()->GetTaskSchedulerInitParams();
-  if (!task_scheduler_init_params)
-    task_scheduler_init_params = GetDefaultTaskSchedulerInitParams();
-  DCHECK(task_scheduler_init_params);
-
-  base::TaskScheduler::CreateAndSetDefaultTaskScheduler(
-      "", *task_scheduler_init_params.get());
+  {
+    auto task_scheduler_init_params =
+        GetContentClient()->browser()->GetTaskSchedulerInitParams();
+    if (!task_scheduler_init_params)
+      task_scheduler_init_params = GetDefaultTaskSchedulerInitParams();
+    DCHECK(task_scheduler_init_params);
+    base::TaskScheduler::GetInstance()->Start(
+        *task_scheduler_init_params.get());
+  }
 
   GetContentClient()->browser()->PerformExperimentalTaskSchedulerRedirections();
 
   base::Thread::Options io_message_loop_options;
   io_message_loop_options.message_loop_type = base::MessageLoop::TYPE_IO;
   base::Thread::Options ui_message_loop_options;
   ui_message_loop_options.message_loop_type = base::MessageLoop::TYPE_UI;
 
   const bool redirect_nonUInonIO_browser_threads =
       GetContentClient()
@@ skipping 779 matching lines @@
         BrowserThread::GetTaskRunnerForThread(BrowserThread::FILE),
         MediaInternals::GetInstance());
   }
   CHECK(audio_manager_);
 
   audio_system_ = media::AudioSystemImpl::Create(audio_manager_.get());
   CHECK(audio_system_);
 }
 
 }  // namespace content