Refactor the dart api a bit:

runtime/bin/builtin.cc

 // Copyright (c) 2011, 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 <stdio.h>
 
 #include "include/dart_api.h"
 
 #include "bin/builtin.h"
 
 // Implementation of native functions which are used for some
 // test/debug functionality in standalone dart mode.
 
 void PrintString(FILE* out, Dart_Handle str) {
-  Dart_Result result = Dart_StringToCString(str);
-  const char* cstring = Dart_IsValidResult(result) ?
-      Dart_GetResultAsCString(result) : Dart_GetErrorCString(result);
+  const char* cstring = NULL;
+  Dart_Handle result = Dart_StringToCString(str, &cstring);
+  if (!Dart_IsValid(result)) {
+      cstring = Dart_GetError(result);
+  }
   fprintf(out, "%s\n", cstring);
   fflush(out);
 }
 
 
 void FUNCTION_NAME(Logger_PrintString)(Dart_NativeArguments args) {
   Dart_EnterScope();
   PrintString(stdout, Dart_GetNativeArgument(args, 0));
   Dart_ExitScope();
 }