Pipe new accessibility Focus Ring interface through mojom to ash

This change preserves the behavior of existing focus rings. It changes
the interface by which information about the focus rings is communicated
from chrome/ to ash/, to allow for additional parameters and multiple
focus rings concurrently, with different visual styles, from a single
extension.

This change does not add full implementation of the additional
parameters. To keep the change size manageable, the implementation
details will be added in a follow-up change.

Bug: 925103
Change-Id: I83ea9767d7de2b451cbce61b4ff48e97629c8e90
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1504504
Commit-Queue: Anastasia Helfinstein <anastasi@google.com>
Reviewed-by: Dominick Ng <dominickn@chromium.org>
Reviewed-by: David Tseng <dtseng@chromium.org>
Cr-Commit-Position: refs/heads/master@{#642281}
12 files changed