[Chromecast] Fix bug when audio device ID is empty string.

chromecast/media/service/cast_renderer.h

 // Copyright 2016 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.
 
 #ifndef CHROMECAST_MEDIA_SERVICE_CAST_RENDERER_H_
 #define CHROMECAST_MEDIA_SERVICE_CAST_RENDERER_H_
 
 #include "base/memory/weak_ptr.h"
 #include "chromecast/media/base/media_resource_tracker.h"
 #include "chromecast/media/base/video_resolution_policy.h"
@@ skipping 49 matching lines @@
   void OnWaitingForDecryptionKey();
   void OnVideoNaturalSizeChange(const gfx::Size& size);
   void OnVideoOpacityChange(bool opaque);
   void CheckVideoResolutionPolicy();
 
   void OnVideoInitializationFinished(const ::media::PipelineStatusCB& init_cb,
                                      ::media::PipelineStatus status);
 
   MediaPipelineBackendFactory* const backend_factory_;
   scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
-  std::string audio_device_id_;
+  const std::string audio_device_id_;
   VideoModeSwitcher* video_mode_switcher_;
   VideoResolutionPolicy* video_resolution_policy_;
   MediaResourceTracker* media_resource_tracker_;
   // Must outlive |pipeline_| to properly count resource usage.
   std::unique_ptr<MediaResourceTracker::ScopedUsage> media_resource_usage_;
 
   ::media::RendererClient* client_;
   CastCdmContext* cast_cdm_context_;
   scoped_refptr<BalancedMediaTaskRunnerFactory> media_task_runner_factory_;
   std::unique_ptr<TaskRunnerImpl> backend_task_runner_;
   std::unique_ptr<MediaPipelineImpl> pipeline_;
   bool eos_[2];
   gfx::Size video_res_;
 
   base::WeakPtrFactory<CastRenderer> weak_factory_;
   DISALLOW_COPY_AND_ASSIGN(CastRenderer);
 };
 
 }  // namespace media
 }  // namespace chromecast
 
 #endif  // CHROMECAST_MEDIA_SERVICE_CAST_RENDERER_H_