Initial import of Blink MediaSource tests.
Make resources paths absolute.
Address CR comments.
Added titles, changed done() overload to add_cleanup() call, changed timeout to explicit_timeout, and changed mp4 & webm order so MP4 is used if it is supported.
Change explicit_timeout back to timeout
Update MP4 files to conform to ISOBMFF movie-fragment relative addressing requirements.
Remove appendStream() test since the STREAMS spec is totally different now and the tests need to be rewritten once support is available.
Remove stale comment.
Merge pull request #725 from acolwell/submission/acolwell/media-source

Initial import of Blink MediaSource tests.