GitLab

Currently ThinWebView background is set to white from the cc::Layer.
This causes a white flash in the video player. This CL adds the ability
to set a background color

Bug: 1151187
Change-Id: I32bcee040d1662a04477feb6b8ac6dc92f652a54
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2552222Reviewed-by: David Trainor <dtrainor@chromium.org>
Commit-Queue: Shakti Sahu <shaktisahu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#830078}