GitLab

As a part of message center restyling, this CL replaces button bar icons
by new vector ones.

Raster back arrow button (notifier settings -> notification list) is
still kept, because it is better to remove the button along with new
settings expand & collapse implementation (see mock).

Font size, color, and paddings are also adjusted following the mock.

This CL changes UI without using switch (i.e. cannot disable the UI
change by switch).

Screenshot (before): http://screen/xGUuGAjgyyT
Screenshot (after): http://screen/t98Ajk0yoN1
Mock: https://crbug.com/726246#c17

TEST=ash_unittests
BUG=726246

Change-Id: I41767e08df4ac56f0dd8525be44c134945ebabea
Reviewed-on: https://chromium-review.googlesource.com/697168Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Reviewed-by: Yoshiki Iguchi <yoshiki@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Commit-Queue: Tetsui Ohkubo <tetsui@chromium.org>
Cr-Commit-Position: refs/heads/master@{#507580}