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

git-svn-id: svn://svn.chromium.org/blink/trunk@176723 bbb929c8-8fbe-4397-9dbb-9b2b20218538