Tom Larsen b7f6be6ff2 Add onLeave callback to DragTarget (#14103)
* Add a callback that fires when a Draggable leaves a DragTarget.  This enables the DragTarget to manage its state from entry to exit.

* It helps to have a null check here

* Add test for onLeave callback and add verbiage to onWillAccept explaining the callback lifecycle of a DragTarget.
2018-01-29 22:48:35 -08:00
..