c.f.  issue 726098 .

Errors from H264Parser, and the Annex B conversion path which uses it, are not surfaced in the media log. This makes it more difficult to debug issues in transmuxers like hls.js.

I'm not certain that it is appropriate for H264Parser to take a MediaLog. If that turns out to be verbose, then we should expose the error information so that higher levels can choose to log it.