Purge AudioOutputDispatcher after close delay if no proxies exist.

media/audio/audio_output_dispatcher_impl.cc

Index: media/audio/audio_output_dispatcher_impl.cc
diff --git a/media/audio/audio_output_dispatcher_impl.cc b/media/audio/audio_output_dispatcher_impl.cc
index 0cb3db85cadf6cb336680055542c6cb40df9e62f..521f91d13342ba8258456660d6135a43847e40ab 100644
--- a/media/audio/audio_output_dispatcher_impl.cc
+++ b/media/audio/audio_output_dispatcher_impl.cc
@@ -130,6 +130,10 @@ void AudioOutputDispatcherImpl::Shutdown() {
   DCHECK(HasOneRef()) << "Only the AudioManager should hold a reference";
 }
 
+bool AudioOutputDispatcherImpl::HasOutputProxies() const {
+  return idle_proxies_ || !proxy_to_physical_map_.empty();
+}
+
 bool AudioOutputDispatcherImpl::CreateAndOpenStream() {
   DCHECK(task_runner_->BelongsToCurrentThread());
   AudioOutputStream* stream = audio_manager_->MakeAudioOutputStream(