overview: Moves all animations to ScopedOverviewAnimationSettings.

Centrallizes all the animation related codes in one spot. Adds new
OVERVIEW_ANIMATION_TYPES as needed.
Also fixes an issue with the drop target widget not animating.
Also replaces some more usages of window selector with overview.

Test: trybots
Bug: 914147
Change-Id: Iaa5e8b26ae68ca0b34e23ac09517d68cb18ee9c3
Reviewed-on: https://chromium-review.googlesource.com/c/1438614
Commit-Queue: Sammie Quon <[email protected]>
Reviewed-by: Xiaoqian Dai <[email protected]>
Reviewed-by: Ahmed Fakhry <[email protected]>
Cr-Commit-Position: refs/heads/master@{#630363}
20 files changed