Final polish of WebView accessibility support for no JavaScript case.

1. Added tests for the new code added by change:I5a796aef

2. WebCore thread now calls the UI thread to set the cursor to
   the current position enabling the user to interact with
   the content that is being selected on the page.

3. Removed the code that changes the selection on movement of the
   cursor ring. We are dropping the "default web view behavior"
   as granularity of reading the document since with this change
   a user can freely access inputs/buttons/links.

Change-Id: I7a3f6677eff0bc95e8127973d07cec78e3465c7b