Remove dart:mirrors from Sky framework

sky/sdk/lib/widgets/basic.dart

 // Copyright 2015 The Chromium Authors. 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:async';
 import 'dart:sky' as sky;
 
 import 'package:vector_math/vector_math.dart';
 
 import '../mojo/asset_bundle.dart';
@@ skipping 566 matching lines @@
 
   void syncRenderObject(Widget old) {
     super.syncRenderObject(old);
     if (old != null) {
       assert(old is WidgetToRenderBoxAdapter);
       assert(root == old.root);
     }
   }
 
   void remove() {
-    RenderObjectWrapper ancestor = findAncestor(RenderObjectWrapper);
+    RenderObjectWrapper ancestor = findAncestorRenderObjectWrapper();
     assert(ancestor is RenderObjectWrapper);
     ancestor.detachChildRoot(this);
     super.remove();
   }
 
 }