Use the browser UI thread for audio on OSX.

media/audio/mac/audio_manager_mac.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 "media/audio/mac/audio_manager_mac.h"
 
 #include <CoreAudio/AudioHardware.h>
 #include <string>
 
 #include "base/bind.h"
@@ skipping 218 matching lines @@
   return audio_device_id;
 }
 
 AudioManagerMac::AudioManagerMac()
     : current_sample_rate_(0) {
   current_output_device_ = kAudioDeviceUnknown;
 
   SetMaxOutputStreamsAllowed(kMaxOutputStreams);
 
   // Task must be posted last to avoid races from handing out "this" to the
-  // audio thread.
+  // audio thread.  Always PostTask even if we're on the right thread since
+  // AudioManager creation is on the startup path and this may be slow.
   GetMessageLoop()->PostTask(FROM_HERE, base::Bind(
       &AudioManagerMac::CreateDeviceListener, base::Unretained(this)));
 }
 
 AudioManagerMac::~AudioManagerMac() {
-  // It's safe to post a task here since Shutdown() will wait for all tasks to
-  // complete before returning.
-  GetMessageLoop()->PostTask(FROM_HERE, base::Bind(
-      &AudioManagerMac::DestroyDeviceListener, base::Unretained(this)));
+  if (GetMessageLoop()->BelongsToCurrentThread()) {
+    DestroyDeviceListener();
+  } else {
+    // It's safe to post a task here since Shutdown() will wait for all tasks to
+    // complete before returning.
+    GetMessageLoop()->PostTask(FROM_HERE, base::Bind(
+        &AudioManagerMac::DestroyDeviceListener, base::Unretained(this)));
+  }
 
   Shutdown();
 }
 
 bool AudioManagerMac::HasAudioOutputDevices() {
   return HasAudioHardware(kAudioHardwarePropertyDefaultOutputDevice);
 }
 
 bool AudioManagerMac::HasAudioInputDevices() {
   return HasAudioHardware(kAudioHardwarePropertyDefaultInputDevice);
@@ skipping 284 matching lines @@
 
 void AudioManagerMac::CreateDeviceListener() {
   DCHECK(GetMessageLoop()->BelongsToCurrentThread());
 
   // Get a baseline for the sample-rate and current device,
   // so we can intelligently handle device notifications only when necessary.
   current_sample_rate_ = HardwareSampleRate();
   if (!GetDefaultOutputDevice(&current_output_device_))
     current_output_device_ = kAudioDeviceUnknown;
 
-  output_device_listener_.reset(new AudioDeviceListenerMac(BindToLoop(
-      GetMessageLoop(), base::Bind(
-          &AudioManagerMac::HandleDeviceChanges,
-          base::Unretained(this)))));
+  output_device_listener_.reset(new AudioDeviceListenerMac(base::Bind(
+      &AudioManagerMac::HandleDeviceChanges, base::Unretained(this))));
 }
 
 void AudioManagerMac::DestroyDeviceListener() {
   DCHECK(GetMessageLoop()->BelongsToCurrentThread());
   output_device_listener_.reset();
 }
 
 void AudioManagerMac::HandleDeviceChanges() {
   int new_sample_rate = HardwareSampleRate();
   AudioDeviceID new_output_device;
   GetDefaultOutputDevice(&new_output_device);
 
   if (current_sample_rate_ == new_sample_rate &&
       current_output_device_ == new_output_device)
     return;
 
   current_sample_rate_ = new_sample_rate;
   current_output_device_ = new_output_device;
   NotifyAllOutputDeviceChangeListeners();
 }
 
 AudioManager* CreateAudioManager() {
   return new AudioManagerMac();
 }
 
 }  // namespace media