Only allow one PIP window between Chrome and Android.

Bug: 841886
Bug: b/69370942
Test: unit test
Test: manually tested Android PIP causing Chrome PIP to close and vice-versa
Change-Id: Ic524db7d48b31d3351a3a669fc48b769a155d956
Reviewed-on: https://chromium-review.googlesource.com/1145148
Reviewed-by: Hidehiko Abe <hidehiko@chromium.org>
Reviewed-by: Luis Hector Chavez <lhchavez@chromium.org>
Commit-Queue: Eliot Courtney <edcourtney@chromium.org>
Cr-Commit-Position: refs/heads/master@{#584689}
9 files changed