GitLab

This change finishes support for AX_ACTION_HIT_TEST in AXHostDelegate
so that you can send a hit test request on the root of the whole automation
tree and get a hit test on either views or web content.

Switches Select-to-speak to use this new API.  A follow-up change will
change the way select-to-speak works so that it sends the mouse event
to the extension and the hit test comes from there, but this is a
self-contained change that can land first.

BUG=699617

Review-Url: https://codereview.chromium.org/2813083003
Cr-Commit-Position: refs/heads/master@{#465716}