To make SniffMP3() more concrete so that we can remove false-positve responses...

To make SniffMP3() more concrete so that we can remove false-positve responses from MPEG-PS streams.

Note: current resync logic keeps searching mp3 frames until it meets a
valid one. This resync logic works well with seek() operation, but in
SniffMP3(), this may cause false-positive classification for the
following MPEG-PS file format.
  A possible MPEG-PS video file:
      [PS header]...[mp3 frame][mp3 frame] ...
  MP3 files:
      [ID3 tag][mp3 frame][mp3 frame] ...

BUG: 5104562
Change-Id: Idd5020723f7bdb2fefc2a63fc8651580fd644399