Add cut and paste to ContentEditable.

 Bug 5806267
 Use visual selection to determine the webkit selection.
 The webkit selection can be used to cut text from an editable
 area. It can also be used to do better complex character text
 copy.

 Webkit change: I194c6d9e2add67151b97092a1a54f5c081296000

Change-Id: I56543d17670a8c98484314c89c7fa6a94cb809e4