Chromecast: adds a media pipeline feeding data to CMA device backends.

The pipeline state transitions are based closely on the interface
of ::media::Renderer. The pipeline interfaces themselves are intended
to be used both renderer- and browser-side, with future renderer-side
implementations using the CMA IPC code for data feeding.,,

Review URL:

Cr-Commit-Position: refs/heads/master@{#305081}
27 files changed