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Continuation of work from crrev.com/c/723422. Previous CL enabled creation of a
locked fullscreen window, and updating a window to locked fullscreen, but it
didn't support removing locked fullscreen from a window.

Design doc @ go/locked-fullscreen-mode

Bug: chromium:755696
Change-Id: Ie9cd6c5944620d260c1f42d327af47b9ac569465
Reviewed-on: https://chromium-review.googlesource.com/769029
Commit-Queue: Ivan Šandrk <isandrk@chromium.org>
Reviewed-by: Istiaque Ahmed <lazyboy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#517090}