Sync volume state using cras signal OutputNodeVolumeChanged.

chromeos/dbus/fake_cras_audio_client.cc

Index: chromeos/dbus/fake_cras_audio_client.cc
diff --git a/chromeos/dbus/fake_cras_audio_client.cc b/chromeos/dbus/fake_cras_audio_client.cc
index 15603915e13955965ddf7cfa9b29027370bf34fe..3ee4c4d45a829f735ae5d2ba5c8aaf77da0a7cb8 100644
--- a/chromeos/dbus/fake_cras_audio_client.cc
+++ b/chromeos/dbus/fake_cras_audio_client.cc
@@ -106,7 +106,10 @@ void FakeCrasAudioClient::GetNodes(const GetNodesCallback& callback,
 }
 
 void FakeCrasAudioClient::SetOutputNodeVolume(uint64_t node_id,
-                                              int32_t volume) {}
+                                              int32_t volume) {
+  if (!notify_volume_change_with_delay_)
+    NotifyOutputNodeVolumeChangedForTesting(node_id, volume);
+}
 
 void FakeCrasAudioClient::SetOutputUserMute(bool mute_on) {
   volume_state_.output_user_mute = mute_on;
@@ -217,6 +220,13 @@ void FakeCrasAudioClient::SetAudioNodesAndNotifyObserversForTesting(
   FOR_EACH_OBSERVER(Observer, observers_, NodesChanged());
 }
 
+void FakeCrasAudioClient::NotifyOutputNodeVolumeChangedForTesting(
+    uint64_t node_id,
+    int volume) {
+  FOR_EACH_OBSERVER(Observer, observers_,
+                    OutputNodeVolumeChanged(node_id, volume));
+}
+
 AudioNodeList::iterator FakeCrasAudioClient::FindNode(uint64_t node_id) {
   return std::find_if(
       node_list_.begin(), node_list_.end(),