GitLab

When MessageCenterView can be scrolled, the 2dp scroll shadow is
displayed at the bottom.

The shadow is displayed over notifications on MessageCenterView.

If MessageCenterView is all scrolled, the shadow is hidden.

BUG=779880

Change-Id: I48fdb3e97c57075114ba4210cea40039c295a6d7
Reviewed-on: https://chromium-review.googlesource.com/923244
Commit-Queue: Megumi Hattori <megumihattori@google.com>
Reviewed-by: Yoshiki Iguchi <yoshiki@chromium.org>
Reviewed-by: Tetsui Ohkubo <tetsui@chromium.org>
Cr-Commit-Position: refs/heads/master@{#537711}