Attempting to remove flakiness from history test

tests/html/history_test.dart

 library HistoryTest;
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_individual_config.dart';
 import 'dart:html';
 
 /// Waits for a callback once, then removes the event handler.
 void expectAsync1Once(EventListenerList list, void callback(arg)) {
   var fn = null;
   fn = expectAsync1((arg) {
     list.remove(fn);
@@ skipping 27 matching lines @@
     });
 
     test('back', () {
       expect(() {
         window.history.pushState(null, document.title, '?dummy1');
         window.history.pushState(null, document.title, '?dummy2');
         var length = window.history.length;
 
         expect(window.location.href.endsWith('dummy2'), isTrue);
 
-        expectAsync1Once(window.on.popState, (_) {
-          expect(window.history.length, length);
-          expect(window.location.href.endsWith('dummy1'), isTrue);
-        });
+        // Need to wait a frame or two to let the pushState events occur.
+        window.setTimeout(expectAsync0(() {
+          expectAsync1Once(window.on.popState, (_) {
+            expect(window.history.length, length);
+            expect(window.location.href.endsWith('dummy1'), isTrue);
+          });
 
-        window.history.back();
+          window.history.back();
+        }), 100);
       }, expectation);
     });
 
     test('replaceState', () {
       expect(() {
         var length = window.history.length;
 
         window.history.replaceState(null, document.title, '?foo=baz');
         expect(window.history.length, length);
         expect(window.location.href.endsWith('foo=baz'), isTrue);
       }, expectation);
     });
   });
 }