GitLab

Wayland does implicit capture. This adds plumbing to track when the
WaylandWindow has implicit capture, and adds function to
PlatformWindow to test for capture.

Also notifies when activation changes.

BUG=none
TEST=covered by tests

Change-Id: I9d73ade6cb8e5e909fe3fe3940eb6f48b0dbd5c7
Reviewed-on: https://chromium-review.googlesource.com/998307
Commit-Queue: Scott Violet <sky@chromium.org>
Reviewed-by: Michael Spang <spang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#548543}