anchor.diff:          ripple1.dispatchEvent(e);
           return new Future(() {}).then((_) {
             var wave = querySelector('.ripple-1 /deep/ .wave');
  -          expect(centerOf(ripple1), centerOf(wave));
  +          expectCloseTo(centerOf(ripple1), centerOf(wave));
           });
         });
   
  
positive.code:   });
  }
  
  centerOf(Element node) {
    var rect = node.getBoundingClientRect();
    return {
      'x': (rect.left + rect.width / 2).floor(),
      'y': (rect.top + rect.height / 2).floor(),
    };
  }
  
negative.code:         ripple2.dispatchEvent(e);
          return new Future(() {}).then((_) {
            var wave = querySelector('.ripple-2 /deep/ .wave');
            expectCloseTo(centerOf(ripple2), centerOf(wave));
          });
        });
  
  