GitLab

Changes in this cl:
1. Update the arrow color while COMPLETEING from SK_ColorWhite to
   gfx::kGoogleGrey100.
2. Add shadow for the circle background. The shadow is the same as
   overscroll affordance.
3. Add burst ripple animation on drag release. The radius of the ripple
   will grow from 40dips to 48dips on this process.

See recorded video:
https://drive.google.com/file/d/0B5I0jFeLxqIiY1JWREN4aW1hSWlocktCOVlwdDV4ZHZyNERN/view?usp=sharing

Bug: 1002733
Change-Id: I96e7836a315c83cbcae415bbd4b359cf6d607501
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1876797
Commit-Queue: Min Chen <minch@chromium.org>
Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Cr-Commit-Position: refs/heads/master@{#709135}