GitLab

Add utility class that handles messages between a Cast SDK client and
the Cast MRP ("internal messages"). The types of internal messages are:
- new session (mrp -> client)
- receiver action (mrp -> client)
- client connect (client -> mrp)
- app message (client <-> mrp)

In particular, client connect should be going away soon (with the use
of PresentationConnection in MRP). app message is bi-directional between
the client and the receiver device, where MRP acts as a pass through.


Also added a utility method to generate a stop session cast channel
message for a given receiver device and session id.


Bug: 809249
Change-Id: I62169dd5b163060464cc6d389c8d93fc4bb2425f
Reviewed-on: https://chromium-review.googlesource.com/1085768Reviewed-by: Bernhard Bauer <bauerb@chromium.org>
Reviewed-by: Brandon Tolsch <btolsch@chromium.org>
Commit-Queue: Derek Cheng <imcheng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577506}