Implement View.cancelDrag

View.cancelDrag cancels a drag operation initiated by
View.startDrag.

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: Iae5ff3534b6c747ae174f170fdd01ff4d3b1c312
6 files changed