Serialize the data argument to History's state-related APIs.

tests/html/history_test.dart

 library HistoryTest;
 import 'package:unittest/unittest.dart';
 import 'package:unittest/html_individual_config.dart';
 import 'dart:html';
 import 'dart:async';
 
 main() {
   useHtmlIndividualConfiguration();
 
   group('supported_state', () {
@@ skipping 16 matching lines @@
         window.history.pushState(null, document.title, '?dummy');
         var length = window.history.length;
 
         window.history.pushState(null, document.title, '?foo=bar');
 
         expect(window.location.href.endsWith('foo=bar'), isTrue);
 
       }, expectation);
     });
 
+    test('pushState with data', () {
+      expect(() {
+        window.history.pushState({'one' : 1}, document.title, '?dummy');
+        expect(window.history.state, equals({'one' : 1}));
+        window.history.pushState(null, document.title, '?foo=bar');
+
+        expect(window.location.href.endsWith('foo=bar'), isTrue);
+
+      }, expectation);
+    });
+
     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);
 
         // Need to wait a frame or two to let the pushState events occur.
         new Timer(const Duration(milliseconds: 100), expectAsync(() {
@@ skipping 28 matching lines @@
       var expectation = HashChangeEvent.supported ? returnsNormally : throws;
       expect(() {
         var event = new HashChangeEvent('change', oldUrl:'old', newUrl: 'new');
         expect(event is HashChangeEvent, true);
         expect(event.oldUrl, 'old');
         expect(event.newUrl, 'new');
       }, expectation);
     });
   });
 }