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Spec : https://mccanny.users.x20web.corp.google.com/www/wm-motion/index.html#overview-freeform
We do not want to move the headers when entering tablet mode, they
should already be at their final destination.

Test: manual
Bug: 812004
Change-Id: Id5ab7e7e4f56da7ecf4c83f76ffa01aa49d6e661
Reviewed-on: https://chromium-review.googlesource.com/958223Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#543149}