media: Use native BufferingState in media mojo interfaces

media/base/buffering_state.h

Index: media/base/buffering_state.h
diff --git a/media/base/buffering_state.h b/media/base/buffering_state.h
index 935922c9b4d7b4b857351e819ca8cf066146cb64..74f8b228ad9f8fd7162ecaf1cdc37a8f9dd4f048 100644
--- a/media/base/buffering_state.h
+++ b/media/base/buffering_state.h
@@ -19,6 +19,8 @@ enum BufferingState {
   //
   // Typical reason is enough data has been prerolled to start playback.
   BUFFERING_HAVE_ENOUGH,
+
+  BUFFERING_STATE_MAX = BUFFERING_HAVE_ENOUGH,
 };
 
 // Used to indicate changes in buffering state;