Add browsertest covering getDisplayMedia() cases

Bug: 326740
Change-Id: I9c75b405e4b5a8a216901df48b5cc41d39ba34fb
Reviewed-on: https://chromium-review.googlesource.com/1187650
Commit-Queue: Emircan Uysaler <emircan@chromium.org>
Reviewed-by: Sergey Ulanov <sergeyu@chromium.org>
Reviewed-by: Christian Fremerey <chfremer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#588730}
3 files changed