chromeos: only hold pointer events if SurfaceId actually changes

BUG=929914
TEST=none

Change-Id: I9174b13bd634ac2e69e5478e5acfe91262c9679a
Reviewed-on: https://chromium-review.googlesource.com/c/1475938
Commit-Queue: Scott Violet <sky@chromium.org>
Commit-Queue: Saman Sami <samans@chromium.org>
Auto-Submit: Scott Violet <sky@chromium.org>
Reviewed-by: Saman Sami <samans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#632837}
1 file changed