The code I landed includes automated tests:
 * content_browsertests:
    MediaSourceTest.Playback_AudioOnly_FLAC_MP4_Unsupported
     (the feature is forced off for this test, playback failure is verified)
    MediaSourceFlacInIsobmffTest.Playback_AudioOnly_FLAC_MP4_Supported
     (the feature is forced on for this test, playback success is verified)
 * media_unittests (with feature forced on):
    MP4StreamParserTest.Flac and Flac192kHz
    PipelineIntegrationTest.MediaSource_FlacInMp4_Hashed

* Also includes audio/mp4 FLAC media capabilities browsertest case,
  though underlying support for CanDecode does not currently
  differentiate kFile vs kMediaSource (TODO added).

You might try (like I did) doing a manual test against BBC's experiment (it's running only for a little while longer now, so try this soon):
http://www.bbc.co.uk/taster/projects/radio-3-concert-sound2

there are some test coverage hole in MSE testing as below:

src= :
Has coverage:
webm
ogv
mp4
opus.ogv
opus.webm
vp9.webm
flac

Miss coverage:
vp9.mp4
vp9+aac.mp4


MSE:
Has coverage:
h264+aac
vp9+vorbis
vp9+vorbis
vp8+opus
vp9+opus

Miss coverage:
flac
mp3
vp9.mp4
vp9+aac.mp4

need work with vasantha to see if these test media files can be added to CDM test suite. If not, we need think of a way to add them to our own test framework