Create a protocol + handler for Background Service recording.

- Create protocol for starting/stopping/querying recording mode
- Add handler which talks to the DevTools context
- Add a SDK model that the view communicates with
- flat_map -> array to avoid multi-thread access issues

Bug: 927726
Change-Id: I11e55a747c7c5c60465508485d6b869b976d40dd
Reviewed-on: https://chromium-review.googlesource.com/c/1477851
Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Commit-Queue: Rayan Kanso <rayankans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#637287}
17 files changed