[Feature] Multimedia Support for Castanets

[Chikdolman]

Multimedia support for Castanets differs from traditional Chromium. In traditional chromium, renderer process reads multimedia stream and decodes using MM pipeline, which then writes to the frame buffer. In Castanets, sending the whole decoded raw stream from a remote renderer process side to a browser process side is a huge burden.

Therefore, a browser process should handle the multimedia stream on its own. The browser process should read multimedia stream, demux and decode AV stream.

[Chikdolman]

@venumusham I discussed this with Mr.Siba. Please reassign to the right person in SRI-B.