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When LayerImpls scroll, their associated transform trees need to be
updated so that they are correct.

This fixes 17 of the 79 failing tests, when verification is turned on.

R=ajuma@chromium.org,vollick@chromium.org
BUG=481585

Review URL: https://codereview.chromium.org/1141353002

Cr-Commit-Position: refs/heads/master@{#330662}