Use the encoding parameter for writeString on RandomAccessFile objects.

runtime/bin/builtin_natives.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 "bin/builtin.h"
 
 #include <stdlib.h>
 #include <string.h>
 
 #include "bin/dartutils.h"
@@ skipping 14 matching lines @@
   V(Directory_Rename, 2)                                                       \
   V(Directory_NewServicePort, 0)                                               \
   V(EventHandler_Start, 1)                                                     \
   V(EventHandler_SendData, 4)                                                  \
   V(Exit, 1)                                                                   \
   V(File_Open, 2)                                                              \
   V(File_Exists, 1)                                                            \
   V(File_Close, 1)                                                             \
   V(File_ReadByte, 1)                                                          \
   V(File_WriteByte, 2)                                                         \
-  V(File_WriteString, 2)                                                       \
   V(File_ReadList, 4)                                                          \
   V(File_WriteList, 4)                                                         \
   V(File_Position, 1)                                                          \
   V(File_SetPosition, 2)                                                       \
   V(File_Truncate, 2)                                                          \
   V(File_Length, 1)                                                            \
   V(File_LengthFromName, 1)                                                    \
   V(File_LastModified, 1)                                                      \
   V(File_Flush, 1)                                                             \
   V(File_Create, 1)                                                            \
@@ skipping 82 matching lines @@
 
 
 void FUNCTION_NAME(Exit)(Dart_NativeArguments args) {
   Dart_EnterScope();
   int64_t status = 0;
   // Ignore result if passing invalid argument and just exit 0.
   DartUtils::GetInt64Value(Dart_GetNativeArgument(args, 0), &status);
   Dart_ExitScope();
   exit(status);
 }