Listen for OutputNodeVolumeChanged signal

chromeos/audio/cras_audio_handler.cc

Index: chromeos/audio/cras_audio_handler.cc
diff --git a/chromeos/audio/cras_audio_handler.cc b/chromeos/audio/cras_audio_handler.cc
index d008d8657792756c4f5995417fb8770780c47cf5..1be1bd2b30062f99a7b5f79db15061a6ab3d43ad 100644
--- a/chromeos/audio/cras_audio_handler.cc
+++ b/chromeos/audio/cras_audio_handler.cc
@@ -562,6 +562,25 @@ void CrasAudioHandler::NodesChanged() {
     GetNodes();
 }
 
+void CrasAudioHandler::OutputNodeVolumeChanged(uint64_t node_id, int volume) {
+  const AudioDevice* device = this->GetDeviceFromId(node_id);
+  int old_volume;
+
+  if (!device || device->is_input)
+    return;
+
+  // If this callback is triggered by a response to previous set volume command,
+  // do nothing.
+  old_volume =
+      static_cast<int>(audio_pref_handler_->GetOutputVolumeValue(device));
+  if (old_volume == volume)
+    return;
+
+  // Otherwise another app or the hardware itself just changed volume, update
+  // the new volume value.
+  SetOutputNodeVolumePercent(node_id, volume);

[jennyz, 2016/05/06 18:11:08]

This will have a glitch for the multiple active nodes case, since it will leave
other active nodes with a different volume node, which might not be the case you
want. You should call CrasAudioHandler::SetOutputVolumePercent to make all the
active nodes set to be same volume level, which is CrasAudioHandler and chromeOS
UI currently assumed.

[hychao, 2016/05/12 08:06:27]

Done.

+}
+
 void CrasAudioHandler::ActiveOutputNodeChanged(uint64_t node_id) {
   if (active_output_node_id_ == node_id)
     return;