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Currently media remoting communicates with extension by text strings
through Media Router mojo API. This CL adds mojo interfaces to allow
CastRemotingConnector in browser talk directly to MediaRemoter in
extension after connected through the Media Router mojo API. These
changes also enable passing the receiver's capablities to remoting
control logic in renderer, which will be done in a follow up CL.

BUG=734672

Review-Url: https://codereview.chromium.org/2951523002
Cr-Commit-Position: refs/heads/master@{#485043}