No removed or inserted text events on static text nodes

Fire only 1 set of text removed/inserted events,
only on the parent hypertext (not on the static text).
This helps avoid redundant live region change announcements.

Bug: 778478
Change-Id: Ic68aab54d46c98576169ecb2146cd6414413e6ac
Reviewed-on: https://chromium-review.googlesource.com/1134199
Commit-Queue: Aaron Leventhal <aleventhal@chromium.org>
Reviewed-by: Dominic Mazzoni <dmazzoni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#574410}
3 files changed