Make Dart_IdentityEqual live up to its sepc and not leak boxing implementation detail. (Reland r275…

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 347 matching lines @@
  *
  * \return The converted string if no error occurs during
  *   the conversion. If an error does occur, an error handle is
  *   returned.
  */
 DART_EXPORT Dart_Handle Dart_ToString(Dart_Handle object);
 
 /**
  * Checks to see if two handles refer to identically equal objects.
  *
- * This is equivalent to using the triple-equals (===) operator.
+ * If both handles refer to instances, this is equivalent to using the top-level
+ * function identical() from dart:core. Otherwise, returns whether the two
+ * argument handles refer to the same object.
  *
  * \param obj1 An object to be compared.
  * \param obj2 An object to be compared.
  *
  * \return True if the objects are identically equal.  False otherwise.
  */
 DART_EXPORT bool Dart_IdentityEquals(Dart_Handle obj1, Dart_Handle obj2);
 
 /**
  * Allocates a handle in the current scope from a persistent handle.
@@ skipping 1891 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 */