Lets the SurfaceLayerBridge commuicate the opacity to the cc layer.

This CL is 1/3 in effort to fix the regressions caused by sending
unneeded compositor frames.

This CL gives the SurfaceLayerBridge control over setting the opacity.
We need this because we will be creating the SurfaceLayer before we have
video, and need to be able to set the opacity to false when we have no
frames.

Bug: 829813
Cq-Include-Trybots: luci.chromium.try:linux_layout_tests_slimming_paint_v2;master.tryserver.blink:linux_trusty_blink_rel
Change-Id: I9eed6b08be0b050ad5c735762d824728263ff091
Reviewed-on: https://chromium-review.googlesource.com/1114092
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: Frank Liberato <liberato@chromium.org>
Reviewed-by: Justin Novosad <junov@chromium.org>
Commit-Queue: CJ DiMeglio <lethalantidote@chromium.org>
Cr-Commit-Position: refs/heads/master@{#570591}