Add Dart_GetNativeReceiver to special case access to the native field

runtime/include/dart_api.h

 /*
  * 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.
  */
 
 #ifndef INCLUDE_DART_API_H_
 #define INCLUDE_DART_API_H_
 
 /** \mainpage Dart Embedding API Reference
@@ skipping 1958 matching lines @@
 
 /**
  * Gets the native instance field of the native argument at some index.
  */
 DART_EXPORT Dart_Handle Dart_GetNativeFieldOfArgument(Dart_NativeArguments args,
                                                       int arg_index,
                                                       int fld_index,
                                                       intptr_t* value);
 
 /**
+ * Gets the native field of the receiver.
+ */
+DART_EXPORT Dart_Handle Dart_GetNativeReceiver(Dart_NativeArguments args,
+                                               intptr_t* value);
+
+/**
  * Sets the return value for a native function.
  */
 DART_EXPORT void Dart_SetReturnValue(Dart_NativeArguments args,
                                      Dart_Handle retval);
 
 DART_EXPORT void Dart_SetBooleanReturnValue(Dart_NativeArguments args,
                                             bool retval);
 
 DART_EXPORT void Dart_SetIntegerReturnValue(Dart_NativeArguments args,
                                             intptr_t retval);
@@ skipping 227 matching lines @@
  *
  * \param object An object.
  * \param peer A value to store in the peer field.
  *
  * \return Returns an error if 'object' is a subtype of Null, num, or
  *   bool.
  */
 DART_EXPORT Dart_Handle Dart_SetPeer(Dart_Handle object, void* peer);
 
 #endif  /* INCLUDE_DART_API_H_ */  /* NOLINT */