Omnibus Observatory UI fixes:

runtime/observatory/tests/observatory_ui/context_ref/element_test.dart

 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:html';
 import 'package:unittest/unittest.dart';
 import 'package:observatory/src/elements/context_ref.dart';
 import '../mocks.dart';
 
 main() {
   ContextRefElement.tag.ensureRegistration();
 
   const isolate = const IsolateRefMock();
   const context = const ContextRefMock();
+  final objects = new ObjectRepositoryMock();
+
   test('instantiation', () {
-    final e = new ContextRefElement(isolate, context);
+    final e = new ContextRefElement(isolate, context, objects);
     expect(e, isNotNull, reason: 'element correctly created');
     expect(e.isolate, equals(isolate));
     expect(e.context, equals(context));
   });
   test('elements created after attachment', () async {
-    final e = new ContextRefElement(isolate, context);
+    final e = new ContextRefElement(isolate, context, objects);
     document.body.append(e);
     await e.onRendered.first;
     expect(e.children.length, isNonZero, reason: 'has elements');
     e.remove();
     await e.onRendered.first;
     expect(e.children.length, isZero, reason: 'is empty');
   });
 }