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As a part of staging the launch of property trees for the compositor
thread, first turn off verification entirely.  The next steps are to
locally fix problems when verification is on for the compositor thread,
and then turn it back on.

Another option would be separate main/compositor thread verification
flags, but that's more complicated.  Additionally, main thread
verification does very little except in a few cc unit tests, as
launching main thread property trees disabled most verification.

Depends on https://codereview.chromium.org/1136643006.

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

Review URL: https://codereview.chromium.org/1134753005

Cr-Commit-Position: refs/heads/master@{#330608}