Ensures that audio tasks cannot run after AudioManager is deleted.

content/browser/browser_main_loop.h

Index: content/browser/browser_main_loop.h
diff --git a/content/browser/browser_main_loop.h b/content/browser/browser_main_loop.h
index 7755d8c1630b9eed826c1fa79631a69ae6da6753..374f9487a9e97a243af5c5c565fef9c812138578 100644
--- a/content/browser/browser_main_loop.h
+++ b/content/browser/browser_main_loop.h
@@ -14,7 +14,6 @@
 #include "build/build_config.h"
 #include "content/browser/browser_process_sub_thread.h"
 #include "content/public/browser/browser_main_runner.h"
-#include "media/audio/audio_manager.h"
 #include "services/resource_coordinator/memory/coordinator/coordinator_impl.h"
 
 #if defined(USE_AURA)
@@ -41,6 +40,7 @@ class DiscardableSharedMemoryManager;
 }
 
 namespace media {
+class AudioManager;
 class AudioSystem;
 #if defined(OS_WIN)
 class SystemMessageWindowWin;
@@ -194,6 +194,8 @@ class CONTENT_EXPORT BrowserMainLoop {
   void EndStartupTracing();
 
   void CreateAudioManager();
+  void DestroyAudioManager();
+
   bool UsingInProcessGpu() const;
 
   void InitializeMemoryManagementComponent();
@@ -295,9 +297,10 @@ class CONTENT_EXPORT BrowserMainLoop {
 
   // |user_input_monitor_| has to outlive |audio_manager_|, so declared first.
   std::unique_ptr<media::UserInputMonitor> user_input_monitor_;
-  // AudioThread needs to outlive |audio_manager_|.
+  std::unique_ptr<media::AudioManager> audio_manager_;
+  // |audio_thread_| must be stopped before |audio_manager_| is deleted so
+  // that tasks referering to the |audio_manager_| cannot be posted.
   std::unique_ptr<AudioManagerThread> audio_thread_;
-  media::ScopedAudioManagerPtr audio_manager_;
   // Calls to |audio_system_| must not be posted to the audio thread if it
   // differs from the UI one.
   std::unique_ptr<media::AudioSystem> audio_system_;