GitLab

In the SingleThreadProxy+SchedulerClient patch,
LayerTreeHostClient::Layout is now called via DoCommit which is called
via Composite(Immediately).  In no cases should the embedder call
Layout() manually.

R=danakj@chromium.org,piman@chromium.org
BUG=none

Review URL: https://codereview.chromium.org/545343003

Cr-Commit-Position: refs/heads/master@{#293632}