GitLab

Since determining occlusion is much more expensive than computing
clipping, throttle the frequency of IntersectionObserver notifications
to no more than one every 100ms.

BUG=827639
R=chrishtr@chromium.org

Change-Id: I6675482041418c628dbddfd648319d18d871d38b
Reviewed-on: https://chromium-review.googlesource.com/1175210Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Reviewed-by: Stefan Zager <szager@chromium.org>
Commit-Queue: Stefan Zager <szager@chromium.org>
Cr-Commit-Position: refs/heads/master@{#585725}