Implement View.cancelDragAndDrop

View.cancelDragAndDrop cancels a drag operation initiated by
View.startDragAndDrop.

It has to be called on a View in the same window (under the
same ViewRootImpl) that the view which started the drag.

Bug: 24415683
Change-Id: If9a265fd8cc4d26b207d582d0d02d5c9ae78eba1
7 files changed