Re-add AC3/EAC3 audio demuxing support

Chrome used to have EAC3/DD+ support (crbug.com/215773),
but it was removed last year (crbug.com/334126). This CL
partially restores the old code and adds AC3 support.
This will allow AC3/EAC3 audio demuxing and can be used
for AC3/EAC3 pass-through support.

BUG=448878

Review URL: https://codereview.chromium.org/812643005

Cr-Commit-Position: refs/heads/master@{#368476}
21 files changed