Don't hide interceptors in mirrors.

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 "package:expect/expect.dart";
 import 'dart:async';
 import 'dart:collection';
 
@@ skipping 161 matching lines @@
   }
   class JSInt extends JSNumber implements int {
   }
   class JSDouble extends JSNumber implements double {
   }
   class JSNull extends Interceptor {
     bool operator==(other) => identical(null, other);
     get hashCode => throw "JSNull.hashCode not implemented.";
     String toString() => 'Null';
     Type get runtimeType => null;
+    noSuchMethod(x) => super.noSuchMethod(x);
   }
   class JSBool extends Interceptor implements bool {
   }
   class JSFunction extends Interceptor implements Function {
   }
   class ObjectInterceptor {
   }
   getInterceptor(x) {}
   getNativeInterceptor(x) {}
   var dispatchPropertyName;
@@ skipping 387 matching lines @@
     } else {
       sourceFile = compiler.sourceFiles[uri.toString()];
     }
     if (sourceFile != null && begin != null && end != null) {
       print(sourceFile.getLocationMessage(message, begin, end, true, (x) => x));
     } else {
       print(message);
     }
   };
 }