[Files app] Add ARIA landmarks for file list and top bar

Files app already have landmark "navigation" for directory tree on the
right hand side. This CL adds 2 more landmarks "contentinfo" for the
top bar that has the breadcrumbs and additional actions like delete.
And "main" for the file list on the right hand side.

ARIA landmark helps users to quickly navigate through those sections
with "Search + ;" shortcut.

Change-Id: I70e9c29538d44a5c5a499d7608549df17321bc7a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1527915
Commit-Queue: Noel Gordon <noel@chromium.org>
Reviewed-by: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#641794}
1 file changed