Repeated live region announcements on Windows

NVDA is announcing live region text changes multiple times. Only fire
one type of live region event at a time.
- Name from attribute change (e.g. from alt, aria-label, aria-labelledby,
etc.): fire only a name change event.
- Text contents change: fire only text removed/inserted events.

Bug: 778478
Change-Id: I7dd17217826fe2ba18bd2c921839bcf19f7d63cf
Reviewed-on: https://chromium-review.googlesource.com/1134021
Commit-Queue: Aaron Leventhal <aleventhal@chromium.org>
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#574875}
13 files changed