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This CL adds support for --tint-composited-content command line flag
that helps to see what content was composited and what went to overlays.

Change-Id: I71e2d72b87be9d37ae0787482a20b531483802f4
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2575827Reviewed-by: Bo <boliu@chromium.org>
Commit-Queue: Vasiliy Telezhnikov <vasilyt@chromium.org>
Cr-Commit-Position: refs/heads/master@{#834215}