Fix off-by-one error in UTF-8 encoding.

sdk/lib/convert/utf.dart

 // Copyright (c) 2013, 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.
 
 part of dart.convert;
 
 /**
  * An instance of the default implementation of the [Utf8Codec].
  *
  * This instance provides a convenient access to the most common UTF-8
@@ skipping 159 matching lines @@
   int _fillBuffer(String str, int start, int end) {
     if (start != end && _isLeadSurrogate(str.codeUnitAt(end - 1))) {
       // Don't handle a trailing lead-surrogate in this loop. The caller has
       // to deal with those.
       end--;
     }
     int stringIndex;
     for (stringIndex = start; stringIndex < end; stringIndex++) {
       int codeUnit = str.codeUnitAt(stringIndex);
       // ASCII has the same representation in UTF-8 and UTF-16.
-      if (codeUnit < _ONE_BYTE_LIMIT) {
+      if (codeUnit <= _ONE_BYTE_LIMIT) {
         if (_bufferIndex >= _buffer.length) break;
         _buffer[_bufferIndex++] = codeUnit;
       } else if (_isLeadSurrogate(codeUnit)) {
         if (_bufferIndex + 3 >= _buffer.length) break;
         // Note that it is safe to read the next code unit. We decremented
         // [end] above when the last valid code unit was a leading surrogate.
         int nextCodeUnit = str.codeUnitAt(stringIndex + 1);
         bool wasCombined = _writeSurrogate(codeUnit, nextCodeUnit);
         if (wasCombined) stringIndex++;
       } else {
@@ skipping 296 matching lines @@
       }
       break loop;
     }
     if (expectedUnits > 0) {
       _value = value;
       _expectedUnits = expectedUnits;
       _extraUnits = extraUnits;
     }
   }
 }