media: Introduce Renderer interface and RendererImpl.

media/filters/audio_renderer_impl.cc

Index: media/filters/audio_renderer_impl.cc
diff --git a/media/filters/audio_renderer_impl.cc b/media/filters/audio_renderer_impl.cc
index 231db851a613213bac38eb39827c7021275c588b..1a6ba155a035effd463e84fd383368f1fb3e5674 100644
--- a/media/filters/audio_renderer_impl.cc
+++ b/media/filters/audio_renderer_impl.cc
@@ -590,7 +590,7 @@ int AudioRendererImpl::Render(AudioBus* audio_bus,
           audio_clock_->CurrentMediaTimestamp(base::TimeDelta()) ==
               audio_clock_->last_endpoint_timestamp()) {
         rendered_end_of_stream_ = true;
-        ended_cb_.Run();
+        task_runner_->PostTask(FROM_HERE, ended_cb_);

[xhwang, 2014/07/25 00:39:29]

Post ended_cb_ so that we don't need to force posting in RendererImpl, as we did
in Pipeline.

       } else if (!received_end_of_stream_ && state_ == kPlaying) {
         if (buffering_state_ != BUFFERING_HAVE_NOTHING) {
           algorithm_->IncreaseQueueCapacity();