[Cast MRP] Created MirroringActivityRecord class.

Bug: 965229
Change-Id: Id1f1c3c703f196514fb77b6362aa2c1dc33d0641
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1605342
Reviewed-by: Takumi Fujimoto <takumif@chromium.org>
Commit-Queue: John Williams <jrw@chromium.org>
Cr-Commit-Position: refs/heads/master@{#661951}
11 files changed