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Depends on https://codereview.chromium.org/1134753005 to turn off
verify_property_trees everywhere so that this doesn't break the world.

This verification is turned off by default, and can be enabled
locally everywhere by reverting the above patch.

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

Review URL: https://codereview.chromium.org/1135393007

Cr-Commit-Position: refs/heads/master@{#330639}