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Previously the settings icon would have its own icon set, but entering
overview would change its icon to the favicon.

Introduce a new window property kHasOverviewIcon which apps that do not
need the favicon would set to true (currently only know to be settings).

Test: manual
Bug: 827619
Change-Id: I9ef99a7491ca3e3513a883c1d84e3e48894ae81a
Reviewed-on: https://chromium-review.googlesource.com/991260Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#548180}