Add method on Value::IsAsyncFunction to detect async functions

include/v8.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 /** \mainpage V8 API Reference Guide
  *
  * V8 is Google's open source JavaScript engine.
  *
  * This set of documents provides reference material generated from the
  * V8 header file, include/v8.h.
@@ skipping 1996 matching lines @@
    * Returns true if this value is a NativeError.
    */
   bool IsNativeError() const;
 
   /**
    * Returns true if this value is a RegExp.
    */
   bool IsRegExp() const;
 
   /**
+   * Returns true if this value is an async function.
+   */
+  bool IsAsyncFunction() const;
+
+  /**
    * Returns true if this value is a Generator function.
    * This is an experimental feature.
    */
   bool IsGeneratorFunction() const;
 
   /**
    * Returns true if this value is a Generator object (iterator).
    * This is an experimental feature.
    */
   bool IsGeneratorObject() const;
@@ skipping 7541 matching lines @@
  */
 
 
 }  // namespace v8
 
 
 #undef TYPE_CHECK
 
 
 #endif  // INCLUDE_V8_H_