Listen for OutputNodeVolumeChanged signal

chromeos/dbus/cras_audio_client.cc

Index: chromeos/dbus/cras_audio_client.cc
diff --git a/chromeos/dbus/cras_audio_client.cc b/chromeos/dbus/cras_audio_client.cc
index acb4bf7f0ff44ae3c73c9a1d259eece4ceb56352..b5d74f153425f30a08ec62cc022972664327d37e 100644
--- a/chromeos/dbus/cras_audio_client.cc
+++ b/chromeos/dbus/cras_audio_client.cc
@@ -245,6 +245,14 @@ class CrasAudioClientImpl : public CrasAudioClient {
                    weak_ptr_factory_.GetWeakPtr()),
         base::Bind(&CrasAudioClientImpl::SignalConnected,
                    weak_ptr_factory_.GetWeakPtr()));
+
+    //
+    cras_proxy_->ConnectToSignal(
+        cras::kCrasControlInterface, "OutputNodeVolumeChanged",
+        base::Bind(&CrasAudioClientImpl::OutputNodeVolumeChangedReceived,
+                   weak_ptr_factory_.GetWeakPtr()),
+        base::Bind(&CrasAudioClientImpl::SignalConnected,
+                   weak_ptr_factory_.GetWeakPtr()));
   }
 
  private:
@@ -309,6 +317,21 @@ class CrasAudioClientImpl : public CrasAudioClient {
     FOR_EACH_OBSERVER(Observer, observers_, ActiveInputNodeChanged(node_id));
   }
 
+  void OutputNodeVolumeChangedReceived(dbus::Signal* signal) {
+    dbus::MessageReader reader(signal);
+    uint64_t node_id;
+    int volume;
+
+    if (!reader.PopUint64(&node_id)) {
+      LOG(ERROR) << "Error eading signal from cras:" << signal->ToString();
+    }
+    if (!reader.PopInt32(&volume)) {
+      LOG(ERROR) << "Error eading signal from cras:" << signal->ToString();
+    }
+    FOR_EACH_OBSERVER(Observer, observers_,
+                      OutputNodeVolumeChanged(node_id, volume));
+  }
+
   void OnGetVolumeState(const GetVolumeStateCallback& callback,
                         dbus::Response* response) {
     bool success = true;