Intiialize AudioManager and related class lazily

media/audio/audio_manager.h

 // 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.
 
 #ifndef MEDIA_AUDIO_AUDIO_MANAGER_H_
 #define MEDIA_AUDIO_AUDIO_MANAGER_H_
 
 #include <memory>
 #include <string>
 
@@ skipping 56 matching lines @@
 
   // A convenience wrapper of AudioManager::Create for testing.
   // The given |task_runner| is shared for both audio io and heavyweight tasks.
   static ScopedAudioManagerPtr CreateForTesting(
       scoped_refptr<base::SingleThreadTaskRunner> task_runner);
 
   // Starts monitoring AudioManager task runner for hangs.
   // Runs the monitor on the given |task_runner|, which must be different from
   // AudioManager::GetTaskRunner to be meaningful.
   // This must be called only after an AudioManager instance is created.
-  static void StartHangMonitor(
+  static void StartHangMonitorIfNeeded(
       scoped_refptr<base::SingleThreadTaskRunner> task_runner);
 
   // Enables non-crash dumps when audio thread hangs are detected.
   // TODO(dalecurtis): There are no callers to this function at present. A list
   // of bad drivers has been given to Microsoft. This should be re-enabled in
   // the future if Microsoft is able to triage third party drivers.
   // See http://crbug.com/422522
   static void EnableCrashKeyLoggingForAudioThreadHangs();
 
 #if defined(OS_LINUX)
@@ skipping 167 matching lines @@
   friend class base::DeleteHelper<AudioManager>;
 
   scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
   scoped_refptr<base::SingleThreadTaskRunner> worker_task_runner_;
   DISALLOW_COPY_AND_ASSIGN(AudioManager);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_AUDIO_AUDIO_MANAGER_H_