Update BufferedDataSource class documentation.

media/blink/buffered_data_source.h

Index: media/blink/buffered_data_source.h
diff --git a/media/blink/buffered_data_source.h b/media/blink/buffered_data_source.h
index fc462b84ef69cf070bb77fbe07c5e7648fcb585d..5b112581d3556a47bea5ea3d6d8d0d12c68d3619 100644
--- a/media/blink/buffered_data_source.h
+++ b/media/blink/buffered_data_source.h
@@ -42,8 +42,7 @@ class MEDIA_EXPORT BufferedDataSourceHost {
 // A data source capable of loading URLs and buffering the data using an
 // in-memory sliding window.
 //
-// BufferedDataSource must be created and initialized on the render thread
-// before being passed to other threads. It may be deleted on any thread.
+// BufferedDataSource must be created and destroyed on the main thread.

[Wez, 2014/11/19 21:45:13]

"main thread" doesn't have any meaning here, does it?

I think you mean "on the supplied |task_runner|" - if so then you can actually
get rid of the |task_runner| parameter and use ThreadTaskRunnerHandle::Get() to
retrieve it in the ctor.

[no sievers, 2014/11/19 21:52:29]

buffered_data_source_unittest.cc passes in another message loop.

 class MEDIA_EXPORT BufferedDataSource : public DataSource {
  public:
   // Used to specify video preload states. They are "hints" to the browser about