Make 'where' lazy.

samples/swarm/swarm_ui_lib/view/CompositeView.dart

 // Copyright (c) 2011, 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.
 
 /**
  * A View that is composed of child views.
  */
 class CompositeView extends View {
 
   List<View> childViews;
@@ skipping 60 matching lines @@
     childViews.add(view);
     // TODO(rnystrom): Container shouldn't be null. Remove this check.
     if (container != null) {
       container.nodes.add(view.node);
     }
     childViewAdded(view);
     return view;
   }
 
   void removeChild(View view) {
-    childViews = childViews.where(bool _(e) { return view != e; });
+    childViews = childViews.where(bool _(e) { return view != e; }).toList();
     // TODO(rnystrom): Container shouldn't be null. Remove this check.
     if (container != null) {
       view.node.remove();
     }
   }
 }