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Implement the currently unimplemented (on mac) NativeWidget::
SetVisibilityAnimationTransition() for this. Autofill uses this
but not constrained windows.

Constrained windows on aura platforms have bespoke animation
suppression code, which is currently different to the desired
behavior on Mac (i.e. the very first "show" should animate).

Consolidate some of the animation logic in MacViews Widgets.

Bug: 767743
Change-Id: If49d139a66873e896e68030f69efdaa81a8dc948
Reviewed-on: https://chromium-review.googlesource.com/1146408Reviewed-by: Michael Wasserman <msw@chromium.org>
Reviewed-by: Sidney San Martín <sdy@chromium.org>
Commit-Queue: Trent Apted <tapted@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577343}