Fix shutdown crash in AudioOutputAuthorizationHandler.

content/browser/renderer_host/media/audio_output_authorization_handler.cc

Index: content/browser/renderer_host/media/audio_output_authorization_handler.cc
diff --git a/content/browser/renderer_host/media/audio_output_authorization_handler.cc b/content/browser/renderer_host/media/audio_output_authorization_handler.cc
index 3bc765fdc86ec5611fa73f2a2e0c39320abae5fb..bbafb5425b26db5956fc29a4c43a2a57767e20cf 100644
--- a/content/browser/renderer_host/media/audio_output_authorization_handler.cc
+++ b/content/browser/renderer_host/media/audio_output_authorization_handler.cc
@@ -34,8 +34,8 @@ media::AudioParameters TryToFixAudioParameters(
 }
 
 media::AudioParameters GetDeviceParametersOnDeviceThread(
+    media::AudioManager* audio_manager,
     const std::string& unique_id) {
-  media::AudioManager* audio_manager = media::AudioManager::Get();
   DCHECK(audio_manager->GetTaskRunner()->BelongsToCurrentThread());
 
   return media::AudioDeviceDescription::IsDefaultDevice(unique_id)
@@ -48,11 +48,13 @@ media::AudioParameters GetDeviceParametersOnDeviceThread(
 namespace content {
 
 AudioOutputAuthorizationHandler::AudioOutputAuthorizationHandler(
+    media::AudioManager* audio_manager,
     MediaStreamManager* media_stream_manager,
     int render_process_id,
     const std::string& salt)
-    : media_stream_manager_(media_stream_manager),
-      permission_checker_(new MediaDevicesPermissionChecker()),
+    : audio_manager_(audio_manager),
+      media_stream_manager_(media_stream_manager),
+      permission_checker_(base::MakeUnique<MediaDevicesPermissionChecker>()),
       render_process_id_(render_process_id),
       salt_(salt),
       weak_factory_(this) {
@@ -189,8 +191,14 @@ void AudioOutputAuthorizationHandler::GetDeviceParameters(
   DCHECK_CURRENTLY_ON(BrowserThread::IO);
   DCHECK(!raw_device_id.empty());
   base::PostTaskAndReplyWithResult(
-      media::AudioManager::Get()->GetTaskRunner(), FROM_HERE,
-      base::Bind(&GetDeviceParametersOnDeviceThread, raw_device_id),
+      // Note: |*audio_manager_| outlives the IO thread, so unretained is safe.

[o1ka, 2016/11/24 13:17:35]

|audio_manager_| is deleted on audio manager thread after IO message loop
destruction.

[Max Morin, 2016/11/24 14:12:20]

Well, it's a bit more complicated since audio manager must not only outlive
posting the task, but also executing the task, which is does since the task to
delete it is posted after the IO thread is stopped.

[o1ka, 2016/11/24 14:34:01]

Yes, it's exactly what I'm pointing to. It's not enough for audio_manager to
outlive the IO thread.
(and remove *)

[Max Morin, 2016/11/24 14:49:03]

Done in the latest patch set.

[o1ka, 2016/11/24 15:11:54]

Acknowledged.

+      // Mac is a special case. On Mac, this task is posted to the UI thread,

[o1ka, 2016/11/24 13:17:35]

because audio managers tuns on UI thread there.

[Max Morin, 2016/11/24 14:12:20]

Done.

+      // but tasks posted to the UI task runner will be ignored when the
+      // shutdown has progressed to deleting the audio manager, so this is still
+      // safe.
+      audio_manager_->GetTaskRunner(), FROM_HERE,
+      base::Bind(&GetDeviceParametersOnDeviceThread,
+                 base::Unretained(audio_manager_), raw_device_id),
       base::Bind(&AudioOutputAuthorizationHandler::DeviceParametersReceived,
                  weak_factory_.GetWeakPtr(), std::move(cb), false,
                  raw_device_id));