[Chromecast] Implement new volume control API

chromecast/media/cma/backend/alsa/media_pipeline_backend_alsa.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chromecast/media/cma/backend/alsa/media_pipeline_backend_alsa.h"
 
 #include <limits>
 
 #include "chromecast/base/task_runner_impl.h"
 #include "chromecast/media/cma/backend/alsa/audio_decoder_alsa.h"
@@ skipping 84 matching lines @@
 
 bool MediaPipelineBackendAlsa::Primary() const {
   return (params_.audio_type !=
           MediaPipelineDeviceParams::kAudioStreamSoundEffects);
 }
 
 std::string MediaPipelineBackendAlsa::DeviceId() const {
   return params_.device_id;
 }
 
+AudioContentType MediaPipelineBackendAlsa::ContentType() const {
+  return params_.content_type;
+}
+
 const scoped_refptr<base::SingleThreadTaskRunner>&
 MediaPipelineBackendAlsa::GetTaskRunner() const {
   return static_cast<TaskRunnerImpl*>(params_.task_runner)->runner();
 }
 
 }  // namespace media
 }  // namespace chromecast