[Shelf] Enable the api to return shelf app icon animation status

This CL adds one additional data member to `ScrollableShelfInfo` to
indicate whether there is any shelf app icon under bounds animation.
This CL facilitates the Tast test to wait until the shelf app icon
animation finishes.

BUG=b:190654715

Change-Id: I98d6d5c72add02ea56d65e167dfbe374df509a94
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3000889
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Andrew Xu <andrewxu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#897938}