New icons are circular an have correct padding.
Replaced 32 and 64px with 48 and 192px icons to cover a wider range
of scales.

Bug: 882176
Test: manual
Change-Id: Ib3d084297bdbd81d778bc15ee64cb1cf8578669a
Reviewed-on: https://chromium-review.googlesource.com/1219774Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Commit-Queue: Vladislav Kaznacheev <kaznacheev@chromium.org>
Cr-Commit-Position: refs/heads/master@{#590359}