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* 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.

R=dmazzoni@google.com

Bug: 866340
Change-Id: I0d3334c39b064afc75ac5e051969fb43a79a0d8a
Reviewed-on: https://chromium-review.googlesource.com/1163724Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Reviewed-by: David Tseng <dtseng@chromium.org>
Commit-Queue: Joanmarie Diggs <joanmarie.diggs@gmail.com>
Cr-Commit-Position: refs/heads/master@{#589951}