Better separation between DragDriver and DragController

Now DragDriver uses DragController through DragDriver.EventListener
interface. I hope that this will make relations between 2 classes clearer,
and will help avoiding mess during future development.

Also, some small cleanups.

Bug: 22609426
Change-Id: Ibaf61804ab931743f2f913fac11bf24ebf9a36c8
2 files changed