Clear all channels to known state before clearing with one masked, so we know what to expect in the masked one. BUG=angleproject:2674 Change-Id: Icbe58615c68e2b282a27d8f29c2f2a48fb8b1c3e Reviewed-on: https://chromium-review.googlesource.com/1212822 Commit-Queue: Yuly Novikov <ynovikov@chromium.org> Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Yuly Novikov <ynovikov@chromium.org>
