function _processMouseLeave() {
    if (this.event.current) {
        this.event.status = 'end';
        this.event.current = 0;
        this.trackedPointerIDs[0] = -1;
        this.triggerGestures();
        this.event.pointers.pop();
    }
}
Treats a mouseleave event as a gesture end.

@method _processMouseLeave
@private

@return {undefined} undefined