Re-land: Emit state-changed:selected events for ATK on Aura Linux

Originally landed:

The revert was due to the two new tests failing on Ubuntu 16.04,
which has a newer version of ATK and thus different expectations.
In order to run the same tests in both environments, prune states
which are not essential to what is being tested from the state set
of the expectations. This modification also eliminates the need to
hand-edit new expectations which are generated on more recent systems.

Original changes preserved in this re-land:
* Add an event notifier in AXPlatformNodeAuraLinux for browser chrome.
* Check to see if focus should follow selection. If it should, also
  emit state-changed:focused events.
* Ensure that the correct states (focusable and selectable) wind up
  in the state set of elements where focus should follow selection.
* Forward events from Blink content to AXPlatformNodeAuraLinux.
* Create an event listener so that DumpAccessibilityEventsTest tests
  can be run. Add expectations for tests for which events are now
  emitted. At the present time, that is only focus and selected.

Bug: 866340
Change-Id: I371ad0a1516aceb6c6924d0142a6f3268dfdd3ac
Reviewed-by: Dominic Mazzoni <>
Commit-Queue: Dominic Mazzoni <>
Cr-Commit-Position: refs/heads/master@{#590209}
15 files changed