Omnibus Observatory UI fixes:

runtime/observatory/tests/observatory_ui/mocks/repositories/object.dart

Index: runtime/observatory/tests/observatory_ui/mocks/repositories/object.dart
diff --git a/runtime/observatory/tests/observatory_ui/mocks/repositories/object.dart b/runtime/observatory/tests/observatory_ui/mocks/repositories/object.dart
new file mode 100644
index 0000000000000000000000000000000000000000..f9656658bc3f15a9a59a88be15323b605db94740
--- /dev/null
+++ b/runtime/observatory/tests/observatory_ui/mocks/repositories/object.dart
@@ -0,0 +1,21 @@
+// Copyright (c) 2017, 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.
+
+part of mocks;
+
+typedef Future<M.Object> ObjectRepositoryMockCallback(
+    M.IsolateRef isolate, String id);
+
+class ObjectRepositoryMock implements M.ObjectRepository {
+  final ObjectRepositoryMockCallback _get;
+
+  ObjectRepositoryMock({ObjectRepositoryMockCallback getter}) : _get = getter;
+
+  Future<M.Object> get(M.IsolateRef isolate, String id, {int count}) {
+    if (_get != null) {
+      return _get(isolate, id);
+    }
+    return new Future.value(null);
+  }
+}