The new borderless icons are based on transparency which works in all
places that have a white background. In some dark mode surfaces, some
dark icons have nearly no contrast. This looks bad, like shown in the
linked bug.

Therefore, this CL reintroduces the white backgrounds. The borders are
still gone on all surfaces.

Bug: 985318
Change-Id: I064b500934b47aecb6321fbacaade461f161c251
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1771967
Commit-Queue: Theresa  <twellington@chromium.org>
Reviewed-by: Theresa  <twellington@chromium.org>
Cr-Commit-Position: refs/heads/master@{#690966}