Dragenter/dragleave events are not fired in time on Linux.

Use attached page to reproduce the issue:
1. Start dragging the purple div.
2. Drag it over yellow area (yellow are should turn red).
3. Do not drag the purple away or drop it - red area will turn green, as if dragleave event was fired.

Affected tests:
com/sun/fx/webnode/tests/dnd/DragAndDrop.java#eventDragenterDragleave