This optimization was the cause of at least one bug (crbug.com/812166), and
will hopefully not be needed once Composite After Paint is implemented.

Bug: 812166
Change-Id: I2024b887949904bad5515d76b2fa29607dae3ff9
Reviewed-on: https://chromium-review.googlesource.com/c/1354572
Commit-Queue: Mason Freed <masonfreed@chromium.org>
Reviewed-by: Chris Harrelson <chrishtr@chromium.org>
Reviewed-by: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#612670}