[chromecast] Moves CastAudioOutputStream::Backend to CMA thread.

chromecast/media/cma/backend/media_pipeline_backend_factory_impl.h

 // Copyright 2017 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_CMA_BACKEND_MEDIA_PIPELINE_BACKEND_FACTORY_H_
-#define CHROMECAST_MEDIA_CMA_BACKEND_MEDIA_PIPELINE_BACKEND_FACTORY_H_
-
-#include <memory>
-#include <string>
+#ifndef CHROMECAST_MEDIA_CMA_BACKEND_MEDIA_PIPELINE_BACKEND_FACTORY_IMPL_H_
+#define CHROMECAST_MEDIA_CMA_BACKEND_MEDIA_PIPELINE_BACKEND_FACTORY_IMPL_H_
 
 #include "base/macros.h"
+#include "chromecast/media/cma/backend/media_pipeline_backend_factory.h"
 
 namespace chromecast {
 namespace media {
 
 class MediaPipelineBackend;
 class MediaPipelineBackendManager;
 struct MediaPipelineDeviceParams;
 
 // Creates MediaPipelineBackends using a given MediaPipelineBackendManager.
-class MediaPipelineBackendFactory {
+class MediaPipelineBackendFactoryImpl : public MediaPipelineBackendFactory {
  public:
   // TODO(slan): Use a static Create method once all of the constructor
   // dependencies are removed from the internal implemenation.
-  explicit MediaPipelineBackendFactory(
+  explicit MediaPipelineBackendFactoryImpl(
       MediaPipelineBackendManager* media_pipeline_backend_manager);
-  virtual ~MediaPipelineBackendFactory();
+  ~MediaPipelineBackendFactoryImpl() override;
 
-  virtual std::unique_ptr<MediaPipelineBackend> CreateBackend(
-      const MediaPipelineDeviceParams& params);
+  std::unique_ptr<MediaPipelineBackend> CreateBackend(
+      const MediaPipelineDeviceParams& params) override;
 
  protected:
   MediaPipelineBackendManager* media_pipeline_backend_manager() {
     return media_pipeline_backend_manager_;
   }
 
  private:
   media::MediaPipelineBackendManager* const media_pipeline_backend_manager_;
 
-  DISALLOW_COPY_AND_ASSIGN(MediaPipelineBackendFactory);
+  DISALLOW_COPY_AND_ASSIGN(MediaPipelineBackendFactoryImpl);
 };
 
 }  // media
 }  // chromecast
 
-#endif  // CHROMECAST_MEDIA_CMA_BACKEND_MEDIA_PIPELINE_BACKEND_FACTORY_H_
+#endif  // CHROMECAST_MEDIA_CMA_BACKEND_MEDIA_PIPELINE_BACKEND_FACTORY_IMPL_H_