Reduce chrome cras dbus call logs during device rebooting.

chromeos/dbus/cras_audio_client.h

Index: chromeos/dbus/cras_audio_client.h
diff --git a/chromeos/dbus/cras_audio_client.h b/chromeos/dbus/cras_audio_client.h
index 23063d8a2b2dc13fd308a9a6a4a619fe7f6d0a87..6d5def26f2207f62676372a9a55e8ccde588f91d 100644
--- a/chromeos/dbus/cras_audio_client.h
+++ b/chromeos/dbus/cras_audio_client.h
@@ -63,11 +63,18 @@ class CHROMEOS_EXPORT CrasAudioClient : public DBusClient {
   // |success| which indicates whether or not the request succeeded.
   typedef base::Callback<void(const AudioNodeList&, bool)> GetNodesCallback;
 
+  // ErrorCallback is used for cras dbus method error response. It receives 2
+  // arguments, |error_name| indicates the dbus error name, and |error_message|
+  // contains the detailed dbus error message.
+  typedef base::Callback<void(const std::string&,
+                              const std::string&)> ErrorCallback;
+
   // Gets the volume state, asynchronously.
   virtual void GetVolumeState(const GetVolumeStateCallback& callback) = 0;
 
   // Gets an array of audio input and output nodes.
-  virtual void GetNodes(const GetNodesCallback& callback) = 0;
+  virtual void GetNodes(const GetNodesCallback& callback,
+                        const ErrorCallback& error_callback) = 0;
 
   // Sets output volume of the given |node_id| to |volume|, in the rage of
   // [0, 100].