 handle_pointerup(e){
        box.releasePointerCapture(e.pointerId);
        if(window.promise_test){
          current_test.step(function(){
            assert_equals(event.buttons, 0,
             'pointerup should happen when all buttons are released.');
            assert_equals(currentPhase, PhaseEnum.WaitingForUp,
              "Current Phase should be " + PhaseEnum.WaitingForUp);
            currentPhase = PhaseEnum.UpDone;
            events.push("target@pointerup");
          });
        }
       