Use the encoding parameter for writeString on RandomAccessFile objects.

runtime/bin/file.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 BIN_FILE_H_
 #define BIN_FILE_H_
 
 #if defined(_WIN32)
 typedef signed __int64 int64_t;
 typedef unsigned __int8 uint8_t;
@@ skipping 50 matching lines @@
     kPositionRequest = 7,
     kSetPositionRequest = 8,
     kTruncateRequest = 9,
     kLengthRequest = 10,
     kLengthFromNameRequest = 11,
     kLastModifiedRequest = 12,
     kFlushRequest = 13,
     kReadByteRequest = 14,
     kWriteByteRequest = 15,
     kReadListRequest = 16,
-    kWriteListRequest = 17,
-    kWriteStringRequest = 18
+    kWriteListRequest = 17
   };
 
   ~File();
 
   // Read/Write attempt to transfer num_bytes to/from buffer. It returns
   // the number of bytes read/written.
   int64_t Read(void* buffer, int64_t num_bytes);
   int64_t Write(const void* buffer, int64_t num_bytes);
 
   // ReadFully and WriteFully do attempt to transfer num_bytes to/from
@@ skipping 64 matching lines @@
 
   static dart::Mutex mutex_;
   static int service_ports_size_;
   static Dart_Port* service_ports_;
   static int service_ports_index_;
 
   DISALLOW_COPY_AND_ASSIGN(File);
 };
 
 #endif  // BIN_FILE_H_