Fix regression with audio mirroring due to observers being added while...

Fix regression with audio mirroring due to observers being added while iterating over the list of observers which causes an infinite loop.

BUG=168362


Review URL: https://chromiumcodereview.appspot.com/11785002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@175282 0039d316-1c4b-4281-b951-d872f2087c98

media/audio/audio_manager_base.cc

@@ -47,6 +47,8 @@ AudioManagerBase::AudioManagerBase()
       max_num_input_streams_(kDefaultMaxInputStreams),
       num_output_streams_(0),
       num_input_streams_(0),
+      output_listeners_(
+          ObserverList<AudioDeviceListener>::NOTIFY_EXISTING_ONLY),
       audio_thread_(new base::Thread("AudioThread")),
       virtual_audio_input_stream_(NULL) {
 #if defined(OS_WIN)