Added new html/LocalStorage test

dart/dom/DartObjectLocalStorage.dart

+#import('../../../../../dart/client/testing/unittest/unittest.dart');
+#import('dart:dom');
+
+verify(var object) {
+  final value = window.document;
+  object.dartObjectLocalStorage = value;
+  final stored = object.dartObjectLocalStorage;
+  Expect.equals(value, stored);
+}
+
+main() {
+  forLayoutTests();
+  test('body', () {
+      HTMLBodyElement body = document.body;
+      verify(body);
+  });
+  test('localStorage', () {
+      Storage storage = window.localStorage;
+      verify(storage);
+  });
+  test('sessionStorage', () {
+      Storage storage = window.sessionStorage;
+      verify(storage);
+  });
+  test('unknown', () {
+      var element = document.createElement('canvas');
+      element.id = 'test';
+      document.body.appendChild(element);
+      element = document.getElementById('test');
+      verify(element);
+  });
+}