This patch introduces two more MP3 test cases to exercise MP3FrameParser:
* vbr-head.mp3: This file contains a Xing header which gives an exact duration
of 10 seconds. However, it only contains 4 MP3 frames total for a real
duration of around 1 second. It is expected that we read the Xing header
and report 10 seconds.
* huge-id3.mp3: This file contains more than 130KB of ID3 tags. When we search
for MP3 frames, we give up after X KB of non-MP3 data. ID3 tags should not
count towards the non-MP3 count, since they can be very large. This test
case makes sure the skipping of ID3 tags works correctly.
