Support for showing/hiding status area volume controls in desktop devices

chrome/browser/chromeos/audio/audio_handler.cc

Index: chrome/browser/chromeos/audio/audio_handler.cc
===================================================================
--- chrome/browser/chromeos/audio/audio_handler.cc	(revision 119435)
+++ chrome/browser/chromeos/audio/audio_handler.cc	(working copy)
@@ -49,8 +49,10 @@
   return g_audio_handler;
 }
 
-bool AudioHandler::IsInitialized() {
-  return mixer_->IsInitialized();
+// static
+AudioHandler* AudioHandler::GetInstanceIfInitialized() {
+  return g_audio_handler && g_audio_handler->IsMixerInitialized() ?
+         g_audio_handler : NULL;
 }
 
 double AudioHandler::GetVolumePercent() {
@@ -60,6 +62,7 @@
 void AudioHandler::SetVolumePercent(double volume_percent) {
   volume_percent = min(max(volume_percent, 0.0), 100.0);
   mixer_->SetVolumeDb(PercentToVolumeDb(volume_percent));
+  FOR_EACH_OBSERVER(VolumeObserver, volume_observers_, OnVolumeChanged());
 }
 
 void AudioHandler::AdjustVolumeByPercent(double adjust_by_percent) {
@@ -74,8 +77,17 @@
 
 void AudioHandler::SetMuted(bool mute) {
   mixer_->SetMuted(mute);
+  FOR_EACH_OBSERVER(VolumeObserver, volume_observers_, OnVolumeChanged());
 }
 
+void AudioHandler::AddVolumeObserver(VolumeObserver* observer) {
+  volume_observers_.AddObserver(observer);
+}
+
+void AudioHandler::RemoveVolumeObserver(VolumeObserver* observer) {
+  volume_observers_.RemoveObserver(observer);
+}
+
 AudioHandler::AudioHandler()
     : mixer_(new AudioMixerAlsa()) {
   mixer_->Init();
@@ -85,6 +97,10 @@
   mixer_.reset();
 };
 
+bool AudioHandler::IsMixerInitialized() {
+  return mixer_->IsInitialized();
+}
+
 // VolumeDbToPercent() and PercentToVolumeDb() conversion functions allow us
 // complete control over how the 0 to 100% range is mapped to actual loudness.
 //