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This CL is a part of the effort to ensure that the target bounds of
the window scaling animation are the shelf icon's final bounds. See
https://crrev.com/c/1996268 for more details. This CL fixes the case 2
by accomplishing the following things:
(1) Updating the visibility state before starting the window scaling
animation. It assures that when the window scaling animation starts,
the target hotseat bounds are already set.
(2) Locking the shelf auto hide state when the back drop widget updates
since the change in back drop widget should not affect the shelf.

This CL should be landed after https://crrev.com/c/2004009 which fixes
the tests broken by this CL.

Bug: 1030819
Change-Id: Iff97f7f1731e7dec6cea36ec99cc3abbee2caa5e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2004052
Commit-Queue: Andrew Xu <andrewxu@chromium.org>
Reviewed-by: Toni Baržić <tbarzic@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#735074}