[Cast MRP] Implemented message passing in in MirroringActivityRecord.

Bug: 965229
Change-Id: I1a35fe6af6a1878b409c7543901ba78bbe7ab2d8
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1623140
Auto-Submit: John Williams <jrw@chromium.org>
Commit-Queue: Brian White <bcwhite@chromium.org>
Reviewed-by: Brian White <bcwhite@chromium.org>
Reviewed-by: Takumi Fujimoto <takumif@chromium.org>
Cr-Commit-Position: refs/heads/master@{#663105}
24 files changed