Drag n drop for stylus

This assumes the gesture used to initiate the drag and drop would be a
stylus touch + button press. This enables stylus users to drop an item
by releasing the button, if it was pressed at the beginning of the drag n
drop. Users could still lift the stylus from the screen to end the drop.

Bug: 19621008
Change-Id: I01051f541bedf006480d46e728498a20f153b322