Fix problems due to unit testing of the compiler.

tests/compiler/dart2js/mock_compiler.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 mock_compiler;
 
 import 'dart:uri';
 
 import '../../../sdk/lib/_internal/compiler/compiler.dart' as api;
 import '../../../sdk/lib/_internal/compiler/implementation/dart2jslib.dart'
@@ skipping 36 matching lines @@
   S() {}
   assertHelper(a){}''';
 
 const String DEFAULT_INTERCEPTORSLIB = r'''
   class JSArray {
     var length;
   }
   class JSString {
     var length;
   }
+  class JSNumber {
+  }
+  class ObjectInterceptor {
+  }
   getInterceptor(x) {}''';
 
 const String DEFAULT_CORELIB = r'''
   print(var obj) {}
   abstract class num {}
   abstract class int extends num { }
   abstract class double extends num { }
   class bool {}
   class String {}
   class Object {}
@@ skipping 190 matching lines @@
   operator []=(Node node, Element element) {
     map[node] = element;
   }
 
   operator [](Node node) => map[node];
 
   void remove(Node node) {
     map.remove(node);
   }
 }