Intiialize AudioManager and related class lazily

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 1459 matching lines @@
   TracingController::GetInstance()->StopTracing(
       TracingController::CreateFileSink(
           startup_trace_file_,
           base::Bind(OnStoppedStartupTracing, startup_trace_file_)));
 }
 
 void BrowserMainLoop::CreateAudioManager() {
   DCHECK(!audio_thread_);
   DCHECK(!audio_manager_);
 
-  bool use_hang_monitor = true;
   audio_manager_ = GetContentClient()->browser()->CreateAudioManager(
       MediaInternals::GetInstance());
   if (!audio_manager_) {
     audio_thread_.reset(new base::Thread("AudioThread"));
 #if defined(OS_WIN)
     audio_thread_->init_com_with_mta(true);
 #endif  // defined(OS_WIN)
     CHECK(audio_thread_->Start());
 #if defined(OS_MACOSX)
     // On Mac audio task runner must belong to the main thread.
     // See http://crbug.com/158170.
-    // Since the audio thread is the UI thread, a hang monitor is not
-    // necessary or recommended.
-    use_hang_monitor = false;
     scoped_refptr<base::SingleThreadTaskRunner> audio_task_runner =
         base::ThreadTaskRunnerHandle::Get();
 #else
     scoped_refptr<base::SingleThreadTaskRunner> audio_task_runner =
         audio_thread_->task_runner();
 #endif  // defined(OS_MACOSX)
     scoped_refptr<base::SingleThreadTaskRunner> worker_task_runner =
         audio_thread_->task_runner();
     audio_manager_ = media::AudioManager::Create(std::move(audio_task_runner),
                                                  std::move(worker_task_runner),
                                                  MediaInternals::GetInstance());
   }
   CHECK(audio_manager_);
-
-  if (use_hang_monitor)
-    media::AudioManager::StartHangMonitor(io_thread_->task_runner());
 }
 
 }  // namespace content