[Cast MRP] Support for DefaultActionPolicy + refactoring related code.

Change-Id: I6dd462281b83f0935b8e6af3a9b9a8d2605d5e44
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1554249
Commit-Queue: John Williams <jrw@chromium.org>
Reviewed-by: Takumi Fujimoto <takumif@chromium.org>
Cr-Commit-Position: refs/heads/master@{#650630}
3 files changed