fix #603, support mock objects

lib/src/js_ast/nodes.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.
 
 part of js_ast;
 
 abstract class NodeVisitor<T> implements TypeRefVisitor<T> {
   T visitProgram(Program node);
 
   T visitBlock(Block node);
@@ skipping 1157 matching lines @@
   List<Identifier> get typeParams;
   /// Return type of this function, if any. `null` otherwise.
   TypeRef get returnType;
 }
 
 class Fun extends FunctionExpression {
   final List<Parameter> params;
   final Block body;
   @override final List<Identifier> typeParams;
   @override final TypeRef returnType;
+
   /** Whether this is a JS generator (`function*`) that may contain `yield`. */
   final bool isGenerator;
 
   final AsyncModifier asyncModifier;
 
   Fun(this.params, this.body, {this.isGenerator: false,
       this.asyncModifier: const AsyncModifier.sync(),
       this.typeParams, this.returnType});
 
   accept(NodeVisitor visitor) => visitor.visitFun(this);
@@ skipping 676 matching lines @@
 
   final List<ModuleItem> body;
   Module(this.body, {this.name});
 
   accept(NodeVisitor visitor) => visitor.visitModule(this);
   void visitChildren(NodeVisitor visitor) {
     for (ModuleItem item in body) item.accept(visitor);
   }
   Module _clone() => new Module(body);
 }