Fix MP4StreamParser discard behavior when retaining 'moof'.

media/mp4/mp4_stream_parser.h

Index: media/mp4/mp4_stream_parser.h
diff --git a/media/mp4/mp4_stream_parser.h b/media/mp4/mp4_stream_parser.h
index b950af2f75b907089843694c1f724368fc6baf3e..c27227e198b1114842feb475dd822760d2fc86d9 100644
--- a/media/mp4/mp4_stream_parser.h
+++ b/media/mp4/mp4_stream_parser.h
@@ -50,7 +50,13 @@ class MEDIA_EXPORT MP4StreamParser : public StreamParser {
 
   bool EmitKeyNeeded(const TrackEncryption& track_encryption);
 
-  bool ReadMDATsUntil(const int64 tgt_tail);
+  // To retain proper framing, each 'mdat' atom must be read; to limit memory
+  // usage, the atom's data needs to be discarded incrementally as frames are
+  // extracted from the stream. This function discards data from the stream up
+  // to |offset|, updating the |mdat_tail_| value so that framing can be
+  // retained after all 'mdat' information has been read.
+  // Returns 'true' on success, 'false' if there was an error.
+  bool ReadAndDiscardMDATsUntil(const int64 offset);
 
   void ChangeState(State new_state);