std-switch: Make focusable by default, and add :focus style

Bug: 972476
Change-Id: I587db2f7491584c875bc43f531a0167c23289894
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1681439
Commit-Queue: Kent Tamura <tkent@chromium.org>
Reviewed-by: Fergal Daly <fergal@chromium.org>
Cr-Commit-Position: refs/heads/master@{#673231}
10 files changed