Add use counter for getDisplayMedia

Bug: 326740
Change-Id: Iea381d99984249796fb0e11279174a553ea9ce8a
Reviewed-on: https://chromium-review.googlesource.com/c/1313328
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Dominick Ng <dominickn@chromium.org>
Reviewed-by: Guido Urdaneta <guidou@chromium.org>
Reviewed-by: Henrik Boström <hbos@chromium.org>
Commit-Queue: Emircan Uysaler <emircan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#605602}
3 files changed