am a063cd64: Merge "Instead of asserting, publish no tracks if an MP3Extractor is used on non-mp3 content." into gingerbread

Merge commit 'a063cd6478254bba3290576ae5556abf469d6535' into gingerbread-plus-aosp

* commit 'a063cd6478254bba3290576ae5556abf469d6535':
  Instead of asserting, publish no tracks if an MP3Extractor is used on non-mp3 content.