Speculatively mitigation for renderer hangs in Scavenger
while waiting in a barrier.

Bug: 
Change-Id: I48520e0ffd99123dbe352d2012c911186c187e4b
Reviewed-on: https://chromium-review.googlesource.com/c/1296463
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Hannes Payer <hpayer@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57130}