Implement updated method overriding rules in the vm.

runtime/lib/string_buffer_patch.dart

 // 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.
 
 patch class StringBuffer {
   /** Backing store for collected UTF-16 code units. */
   Uint16List _buffer;
   /** Number of code units collected. */
   int _length = 0;
   /**
@@ skipping 29 matching lines @@
     if (str.isEmpty) return;
     _ensureCapacity(str.length);
     for (int i = 0; i < str.length; i++) {
       int unit = str.codeUnitAt(i);
       _buffer[_length + i] = unit;
       _codeUnitMagnitude |= unit;
     }
     _length += str.length;
   }
 
-  /* patch */ writeCharCode(int charCode) {
+  /* patch */ void writeCharCode(int charCode) {
     if (charCode <= 0xFFFF) {
       if (charCode < 0) {
         throw new RangeError.range(charCode, 0, 0x10FFFF);
       }
       _ensureCapacity(1);
       _buffer[_length++] = charCode;
       _codeUnitMagnitude |= charCode;
     } else {
       if (charCode > 0x10FFFF) {
         throw new RangeError.range(charCode, 0, 0x10FFFF);
@@ skipping 37 matching lines @@
     newBuffer.setRange(0, _length, _buffer);
     _buffer = newBuffer;
   }
 
   /**
    * Create a [String] from the UFT-16 code units in buffer.
    */
   static String _create(Uint16List buffer, int length, bool isLatin1)
       native "StringBuffer_createStringFromUint16Array";
 }