[pip] Add ArcPipBridge.

Currently this only contains some basic things for telling Chrome when
Android PIP has started or finished, but later we may add more.

Bug: 841886
Bug: b/69370942
Test: compiles and ARC runs. ArcPipBridge comes up as well.
Change-Id: I14ac5b6d8628c4cc2f571f06690e6d3c228d943d
Reviewed-on: https://chromium-review.googlesource.com/1120085
Commit-Queue: Eliot Courtney <edcourtney@chromium.org>
Reviewed-by: Mattias Nissler <mnissler@chromium.org>
Reviewed-by: Luis Hector Chavez <lhchavez@chromium.org>
Cr-Commit-Position: refs/heads/master@{#576803}
12 files changed