[CrOS PhoneHub] Fix quick action bottom padding.

This CL fixes the bottom padding of the quick action view when there are
no continue browsing chips shown below.

Screenshots:
https://screenshot.googleplex.com/3L2rq3Z2WPYhNgN.png (before)
https://screenshot.googleplex.com/8TxuihZsi4TZobu.png (after)

BUG=1106937,1126208

Change-Id: I8cfd9d60d72951ef1341f69e910f4b4e46285297
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2495676
Commit-Queue: Meilin Wang <meilinw@chromium.org>
Reviewed-by: Kyle Horimoto <khorimoto@chromium.org>
Reviewed-by: Tim Song <tengs@chromium.org>
Cr-Commit-Position: refs/heads/master@{#821069}