Use a signed 32-bit integer for representing code points.

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
  *
  * Dart is a class-based programming language for creating structured
@@ skipping 1370 matching lines @@
 
 /**
  * Returns a String built from an array of UTF-32 encoded characters.
  *
  * \param utf32_array An array of UTF-32 encoded characters.
  * \param length The length of the codepoints array.
  *
  * \return The String object if no error occurs. Otherwise returns
  *   an error handle.
  */
-DART_EXPORT Dart_Handle Dart_NewStringFromUTF32(const uint32_t* utf32_array,
+DART_EXPORT Dart_Handle Dart_NewStringFromUTF32(const int32_t* utf32_array,
                                                 intptr_t length);
 
 /**
  * Is this object an external String?
  *
  * An external String is a String which references a fixed array of
  * codepoints which is external to the Dart heap.
  */
 DART_EXPORT bool Dart_IsExternalString(Dart_Handle object);
 
@@ skipping 1369 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_