[Chromeshine] Mark WebContents as obscured for a11y

It wasn't sufficient to call updateAccessibilityVisibility, since that doesn't
account for SuspendedTab obscuring the WebContents, only SadTab. Rather than
moving knowledge of SuspendedTab into Tab.java, we can just directly mark the
WebContents as obscured ourselves.

Bug: 978596
Change-Id: I725a153b61124385cb746d2f557695620185dac0
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1741311
Commit-Queue: Patrick Noland <pnoland@chromium.org>
Reviewed-by: Natalie Chouinard <chouinard@chromium.org>
Cr-Commit-Position: refs/heads/master@{#685049}
2 files changed