[chromecast] Pass media task runner to MediaPipelineBackendManager.

chromecast/media/cma/backend/media_pipeline_backend_manager.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_CMA_BACKEND_MEDIA_PIPELINE_BACKEND_MANAGER_H_
 #define CHROMECAST_MEDIA_CMA_BACKEND_MEDIA_PIPELINE_BACKEND_MANAGER_H_
 
 #include <map>
 #include <vector>
 
 #include "base/macros.h"
+#include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
+#include "base/single_thread_task_runner.h"
 #include "chromecast/public/media/media_pipeline_backend.h"
 #include "chromecast/public/media/media_pipeline_device_params.h"
 
-namespace base {
-template <typename T>
-struct DefaultLazyInstanceTraits;
-}  // namespace base
-
 namespace chromecast {
 namespace media {
 
 // This class manages created media pipelines, and provides volume control by
 // stream type.
 // All functions in this class should be called on the media thread.
 class MediaPipelineBackendManager {
  public:
+  explicit MediaPipelineBackendManager(
+      scoped_refptr<base::SingleThreadTaskRunner> media_task_runner);
+  ~MediaPipelineBackendManager();
+
   // Create media pipeline backend.
-  static MediaPipelineBackend* CreateMediaPipelineBackend(
+  scoped_ptr<MediaPipelineBackend> CreateMediaPipelineBackend(
       const MediaPipelineDeviceParams& params);
 
   // Create media pipeline backend with a specific stream_type.
-  static MediaPipelineBackend* CreateMediaPipelineBackend(
+  scoped_ptr<MediaPipelineBackend> CreateMediaPipelineBackend(
       const MediaPipelineDeviceParams& params,
       int stream_type);
 
-  // Internal clean up when a new media pipeline backend is destroyed.
-  static void OnMediaPipelineBackendDestroyed(
-      const MediaPipelineBackend* backend);
-
   // Sets the relative volume for a specified stream type,
   // with range [0.0, 1.0] inclusive. If |multiplier| is outside the
   // range [0.0, 1.0], it is clamped to that range.
   // TODO(tianyuwang): change stream_type to use a enum.
-  static void SetVolumeMultiplier(int stream_type, float volume);
+  void SetVolumeMultiplier(int stream_type, float volume);
+
+  base::SingleThreadTaskRunner* task_runner() const {
+    return media_task_runner_.get();
+  }
 
  private:
-  friend struct base::DefaultLazyInstanceTraits<MediaPipelineBackendManager>;
+  friend class MediaPipelineBackendWrapper;
 
-  // Returns a pointer to a singleton instance of the
-  // MediaPipelineBackendManager.
-  static MediaPipelineBackendManager* Get();
-
-  MediaPipelineBackendManager();
-  ~MediaPipelineBackendManager();
+  // Internal clean up when a new media pipeline backend is destroyed.
+  void OnMediaPipelineBackendDestroyed(const MediaPipelineBackend* backend);
 
   float GetVolumeMultiplier(int stream_type);
 
+  const scoped_refptr<base::SingleThreadTaskRunner> media_task_runner_;
+
   // A vector that stores all of the existing media_pipeline_backends_.
   std::vector<MediaPipelineBackend*> media_pipeline_backends_;
 
   // Volume multiplier for each type of audio streams.
   std::map<int, float> volume_by_stream_type_;
 
   DISALLOW_COPY_AND_ASSIGN(MediaPipelineBackendManager);
 };
 
 }  // namespace media
 }  // namespace chromecast
 
 #endif  // CHROMECAST_MEDIA_CMA_BACKEND_MEDIA_PIPELINE_BACKEND_MANAGER_H_