Lookup super scope after looking up lexical scope.

frog/leg/resolver.dart

 // Copyright (c) 2012, 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.
 
 interface TreeElements {
   Element operator[](Node node);
   Selector getSelector(Send send);
 }
 
 class TreeElementMapping implements TreeElements {
@@ skipping 1535 matching lines @@
 class ClassScope extends Scope {
   ClassScope(ClassElement element, LibraryElement library)
     : super(new TopScope(library), element);
 
   Element lookup(SourceString name) {
     ClassElement cls = element;
     Element element = cls.lookupLocalMember(name);
     if (element != null) return element;
     element = parent.lookup(name);
     if (element != null) return element;
-    // TODO(ngeoffray): Lookup in the super class.
-    return null;
+    return cls.lookupSuperMember(name);
   }
 
   Element add(Element element) {
     throw "Cannot add an element in a class scope";
   }
 }
 
 class TopScope extends Scope {
   LibraryElement get library() => element;
 
   TopScope(LibraryElement library) : super(null, library);
   Element lookup(SourceString name) => library.find(name);
 
   Element add(Element element) {
     throw "Cannot add an element in the top scope";
   }
 }