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

runtime/vm/dart_api_impl.cc

 // 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.
 
 #include "include/dart_api.h"
 
 #include "vm/bigint_operations.h"
 #include "vm/class_finalizer.h"
 #include "vm/compiler.h"
 #include "vm/dart.h"
@@ skipping 1553 matching lines @@
   Isolate* isolate = Isolate::Current();
   DARTSCOPE(isolate);
   if (utf16_array == NULL && length != 0) {
     RETURN_NULL_ERROR(utf16_array);
   }
   CHECK_LENGTH(length, String::kMaxElements);
   return Api::NewHandle(isolate, String::New(utf16_array, length));
 }
 
 
-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) {
   Isolate* isolate = Isolate::Current();
   DARTSCOPE(isolate);
   if (utf32_array == NULL && length != 0) {
     RETURN_NULL_ERROR(utf32_array);
   }
   CHECK_LENGTH(length, String::kMaxElements);
   return Api::NewHandle(isolate, String::New(utf32_array, length));
 }
 
@@ skipping 2907 matching lines @@
   }
   {
     NoGCScope no_gc;
     RawObject* raw_obj = obj.raw();
     isolate->heap()->SetPeer(raw_obj, peer);
   }
   return Api::Success(isolate);
 }
 
 }  // namespace dart