Overview animation improvements

* Apply Blur/Sield animation after transform animation.
* Skip blur animation if the wallapper already have the target blur sigma.

I moved ShouldAnimateWallpaper to OverviewGrid.

Bug: 924396, 924221
Test: covered by unit tests.

Change-Id: Ib2a07484efada16b2487be9b943549b237004505
Reviewed-on: https://chromium-review.googlesource.com/c/1432881
Commit-Queue: Mitsuru Oshima <oshima@chromium.org>
Reviewed-by: Sammie Quon <sammiequon@chromium.org>
Cr-Commit-Position: refs/heads/master@{#626031}
10 files changed