Truley compute direct subtypes of native classes.

lib/compiler/implementation/native_handler.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.
 
 #library('native');
 #import('dart:uri');
 #import('leg.dart');
 #import('elements/elements.dart');
 #import('scanner/scannerlib.dart');
 #import('ssa/ssa.dart');
 #import('tree/tree.dart');
 #import('util/util.dart');
 
 void processNativeClasses(Compiler compiler,
                           Collection<LibraryElement> libraries) {
   for (LibraryElement library in libraries) {
     processNativeClassesInLibrary(compiler, library);
   }
 }
 
 void addSubtypes(ClassElement cls,
                  NativeEmitter emitter) {
   for (Type type in cls.allSupertypes) {
     List<Element> subtypes = emitter.subtypes.putIfAbsent(
         type.element,
         () => <ClassElement>[]);
     subtypes.add(cls);
   }
+
+  List<Element> directSubtypes = emitter.directSubtypes.putIfAbsent(
+      cls.superclass,
+      () => <ClassElement>[]);
+  directSubtypes.add(cls);
 }
 
 void processNativeClassesInLibrary(Compiler compiler,
                                    LibraryElement library) {
   bool hasNativeClass = false;
   for (Link<Element> link = library.topLevelElements;
        !link.isEmpty(); link = link.tail) {
     Element element = link.head;
     if (element.kind == ElementKind.CLASS) {
       ClassElement classElement = element;
@@ skipping 297 matching lines @@
                                       String parameters) {     
   buffer.add("  if (Object.getPrototypeOf(this).hasOwnProperty");
   buffer.add("('$methodName')) {\n");
   buffer.add("  $code");
   buffer.add("  } else {\n");
   buffer.add("    return Object.prototype.$methodName.call(this");
   buffer.add(parameters == '' ? '' : ', $parameters');
   buffer.add(");\n");
   buffer.add("  }\n");
 }