Support promises for fullscreen API.

Add ability to store the promises in the pending requests and exits.

Adjust tests to ensure they work correctly with promises.

BUG=383813

Change-Id: I81e4780d5ea25b3a1ac7fef54b1fbc9c0d31897a
Reviewed-on: https://chromium-review.googlesource.com/1075711
Commit-Queue: Dave Tapuska <dtapuska@chromium.org>
Reviewed-by: Philip Jägenstedt <foolip@chromium.org>
Cr-Commit-Position: refs/heads/master@{#562946}
18 files changed