Support for extending native classes

tests/utils/dummy_compiler_test.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.
 // VMOptions=
 // VMOptions=--print-object-histogram
 
 // Smoke test of the dart2js compiler API.
 library dummy_compiler;
 
 import 'dart:async';
@@ skipping 58 matching lines @@
   var toString;
 }
 class JSFunction {}
 class JSInt {}
 class JSDouble {}
 class JSNumber {}
 class JSNull {}
 class JSBool {}
 getInterceptor(o){}
 getDispatchProperty(o) {}
-setDispatchProperty(o, v) {}""";
+setDispatchProperty(o, v) {}
+var mapTypeToInterceptor;""";
     } else if (uri.path.endsWith('js_helper.dart')) {
       source = 'library jshelper; class JSInvocationMirror {} '
                'class ConstantMap {} class TypeImpl {} '
                'createRuntimeType(String name) => null;';
     } else if (uri.path.endsWith('isolate_helper.dart')) {
       source = 'library isolatehelper; class _WorkerStub {}';
     } else {
       source = "library lib;";
     }
   } else {
@@ skipping 17 matching lines @@
               new Uri(scheme: 'package', path: '/'),
               provider, handler);
   result.then((String code) {
     if (code == null) {
       throw 'Compilation failed';
     }
   }, onError: (e) {
       throw 'Compilation failed';
   });
 }