Load CMA backend from shared library

chromecast/public/media/media_pipeline_device_params.h

 // Copyright 2014 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_DEVICE_PARAMS_H_
-#define CHROMECAST_MEDIA_CMA_BACKEND_MEDIA_PIPELINE_DEVICE_PARAMS_H_
+#ifndef CHROMECAST_PUBLIC_MEDIA_MEDIA_PIPELINE_DEVICE_PARAMS_H_
+#define CHROMECAST_PUBLIC_MEDIA_MEDIA_PIPELINE_DEVICE_PARAMS_H_
 
-#include "base/macros.h"
+#include "task_runner.h"
 
 namespace chromecast {
 namespace media {
 
-class MediaPipelineDeviceParams {
- public:
+// Supplies creation parameters to platform-specific pipeline backend.
+struct MediaPipelineDeviceParams {
   enum MediaSyncType {
     // Default operation, synchronize playback using PTS with higher latency.
     kModeSyncPts = 0,
     // With this mode, synchronization is disabled and audio/video frames are
     // rendered "right away":
     // - for audio, frames are still rendered based on the sampling frequency
     // - for video, frames are rendered as soon as available at the output of
     //   the video decoder.
     //   The assumption is that no B frames are used when synchronization is
     //   disabled, otherwise B frames would always be skipped.
     kModeIgnorePts = 1,
     // In addition to the constraints above, also do not wait for vsync.
     kModeIgnorePtsAndVSync = 2,
   };
 
-  MediaPipelineDeviceParams();
-  ~MediaPipelineDeviceParams();
+  MediaPipelineDeviceParams(TaskRunner* task_runner_in)
+      : sync_type(kModeSyncPts), task_runner(task_runner_in) {}
 
-  MediaSyncType sync_type;
+  MediaPipelineDeviceParams(MediaSyncType sync_type_in,
+                            TaskRunner* task_runner_in)
+      : sync_type(sync_type_in), task_runner(task_runner_in) {}
+
+  const MediaSyncType sync_type;
+
+  // task_runner allows backend implementations to post tasks to the media
+  // thread.  Since all calls from cast_shell into the backend are made on
+  // the media thread, this may simplify thread management and safety for
+  // some backends.
+  TaskRunner* const task_runner;
 };
 
 }  // namespace media
 }  // namespace chromecast
 
 #endif  // CHROMECAST_MEDIA_CMA_BACKEND_MEDIA_PIPELINE_DEVICE_PARAMS_H_