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Ensures that the view stays black until webpage style data is loaded and
parsed, by setting up a black background layer and making content
output surfaces initially transparent.

Some IWYU fixes.

Bug: 1051241
Change-Id: I22552863c1ae7cb2b7df280a4936a65445614215
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2123307
Commit-Queue: Kevin Marshall <kmarshall@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Reviewed-by: David Dorwin <ddorwin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#755213}