Granular navigation not possible in edit text if the view has content description.

1. We were giving precedence of content description over text and this is
   what content description is supposed to do - override the text. However,
   putting content description on an EditText by mistake would render the
   text view not navigable which is pretty much unusable. Now we are giving
   precedence to the text and use the content description as a fall back if
   text is empty.

bug:7078382

Change-Id: I00882ace149344478b127124bd5e641903e1b756