Add ResizeObserver use counter

Bug: 612962
Change-Id: I794b3010dd4d234f81be025987cda38b134aae4e
Reviewed-on: https://chromium-review.googlesource.com/c/1279355
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Commit-Queue: Chris Harrelson <chrishtr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#599491}
3 files changed