Fix widget.dart to work with the latest web_ui library. Specifically, query selectors need to use "…

test/effects/swapper_tests.dart

 part of effects_tests;
 
 // TODO: support case where many children, but invalid child called to show
 //       need to specify that all of the original children will still be shown
 
 void registerSwapperTests() {
   group('Swapper', () {
     tearDown(_cleanUpPlayground);
 
     _swapperTest(1, [], 0, true, 0);
@@ skipping 92 matching lines @@
           expect(actualResult, expectedResult);
         }))
         .then((_) => _getDisplayedIndicies(pg))
         .then(expectAsync1((List<int> displayedIndicies) {
           if(expectedDisplayed == null) {
             expect(displayedIndicies, isEmpty, reason: 'There are no items to display');
           } else {
             expect(displayedIndicies.length, 1, reason: 'there should only be one displayed item');
             expect(displayedIndicies[0], expectedDisplayed);
           }
-        }), onError: (AsyncError error) {
+        }), onError: (error) {
           registerException(error.error, error.stackTrace);
         });
     }
   });
 }
 
 /**
  * get the list of all children of [host] that are currently 'shown'
  * assume all animations on all children are finished
  */
@@ skipping 12 matching lines @@
 }
 
 void _addTestElementToPlayground(String text, bool hidden) {
   final display = hidden ? 'none' : 'block';
   _getPlayground().children.add(
       new DivElement()
         ..text = text
         ..style.cssText = 'background: pink; width: 100px; height: 100px; display: $display;'
         );
 }