Adds CHECKs to ensure that AudioManager is valid.

During the construction of AudioOutputController, AudioManager must
still be valid. AudioOutputController instances are created on the
IO thread, which is stopped before AudioManager is destroyed.

BUG=606234

Review-Url: https://codereview.chromium.org/1991483002
Cr-Commit-Position: refs/heads/master@{#394296}

content/browser/renderer_host/media/audio_renderer_host.cc

@@ -242,6 +242,7 @@ void AudioRendererHost::GetOutputControllers(
 }
 
 void AudioRendererHost::OnChannelClosing() {
+  DCHECK_CURRENTLY_ON(BrowserThread::IO);
   // Since the IPC sender is gone, close all requested audio streams.
   while (!audio_entries_.empty()) {
     // Note: OnCloseStream() removes the entries from audio_entries_.

media/audio/audio_output_controller.cc

@@ -59,10 +59,11 @@ scoped_refptr<AudioOutputController> AudioOutputController::Create(
     const AudioParameters& params,
     const std::string& output_device_id,
     SyncReader* sync_reader) {
-  DCHECK(audio_manager);
+  CHECK(audio_manager);
+  CHECK_EQ(AudioManager::Get(), audio_manager);
   DCHECK(sync_reader);
 
-  if (!params.IsValid() || !audio_manager)
+  if (!params.IsValid())
     return NULL;
 
   scoped_refptr<AudioOutputController> controller(new AudioOutputController(
@@ -73,28 +74,33 @@ scoped_refptr<AudioOutputController> AudioOutputController::Create(
 }
 
 void AudioOutputController::Play() {
+  CHECK_EQ(AudioManager::Get(), audio_manager_);
   message_loop_->PostTask(FROM_HERE, base::Bind(
       &AudioOutputController::DoPlay, this));
 }
 
 void AudioOutputController::Pause() {
+  CHECK_EQ(AudioManager::Get(), audio_manager_);
   message_loop_->PostTask(FROM_HERE, base::Bind(
       &AudioOutputController::DoPause, this));
 }
 
 void AudioOutputController::Close(const base::Closure& closed_task) {
+  CHECK_EQ(AudioManager::Get(), audio_manager_);
   DCHECK(!closed_task.is_null());
   message_loop_->PostTaskAndReply(FROM_HERE, base::Bind(
       &AudioOutputController::DoClose, this), closed_task);
 }
 
 void AudioOutputController::SetVolume(double volume) {
+  CHECK_EQ(AudioManager::Get(), audio_manager_);
   message_loop_->PostTask(FROM_HERE, base::Bind(
       &AudioOutputController::DoSetVolume, this, volume));
 }
 
 void AudioOutputController::GetOutputDeviceId(
     base::Callback<void(const std::string&)> callback) const {
+  CHECK_EQ(AudioManager::Get(), audio_manager_);
   base::PostTaskAndReplyWithResult(
       message_loop_.get(),
       FROM_HERE,
@@ -104,6 +110,7 @@ void AudioOutputController::GetOutputDeviceId(
 
 void AudioOutputController::SwitchOutputDevice(
     const std::string& output_device_id, const base::Closure& callback) {
+  CHECK_EQ(AudioManager::Get(), audio_manager_);
   message_loop_->PostTaskAndReply(
       FROM_HERE,
       base::Bind(&AudioOutputController::DoSwitchOutputDevice, this,