Reland: Make 'click' the default action of unfocusable ARIA buttons

Trusty comes with a version of ATK that does not support the checkable
attribute, so we must specifically deny this in the test. A followup
change will make this global in order to avoid having to add it to many
tests.

Original commit message:
> Users of ATs on AuraLinux use the default action to know whether or not
> to activate nodes via the keyboard or a simulated mouse event. When a
> node with a button role cannot receive keyboard focus, have the default
> action be click. This heuristic helps ensure that when there is an ARIA
> button that cannot be activated via the keyboard, users know to simulate
> a mouse click.

Bug: 1025264
Change-Id: Ib8e66b369e30c771ce8533de24050f99e32ab579
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1953709
Reviewed-by: Joanmarie Diggs <jdiggs@igalia.com>
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Commit-Queue: Martin Robinson <mrobinson@igalia.com>
Cr-Commit-Position: refs/heads/master@{#722496}
7 files changed