Revert 176723 "Revert 172948 "Don't send accessibility notificat..."

Un-reverting this change that was temporarily reverted for a branch merge.

> Revert 172948 "Don't send accessibility notifications for a doc ..."
> 
> Temporarily reverting so that we can merge the revert to M36. Will un-revert
> on trunk.
> 
> > Don't send accessibility notifications for a doc with an empty/blank url.
> > 
> > This is a refinement to the change that started sending
> > accessibility notifications early. This also addresses
> > the test for this change that was flaky.
> > 
> > BUG=353067,363235
> > NOTRY=true
> > 
> > Review URL: https://codereview.chromium.org/242103012
> 
> TBR=dmazzoni@chromium.org
> 
> Review URL: https://codereview.chromium.org/353443002

TBR=dmazzoni@google.com

Review URL: https://codereview.chromium.org/345403004

git-svn-id: svn://svn.chromium.org/blink/trunk@176729 bbb929c8-8fbe-4397-9dbb-9b2b20218538