Fix auto-complete for content-editable fields.

 Bug 5608192
 Text content for content-editable fields is
 retrieved and given to the WebViewInputConnection
 so that suggestions will work appropriately.
 Edits with WebViewInputConnection uses
 replaceTextfieldText just like WebTextView.

 Webkit Change: Idcf8d99d9e844669ea68122a7509990f5ce8dcca

Change-Id: I5f1fcc13a0abe204db301e027954dc47c3a48db0