Fix UTF8 encoder for Unicode runes > 0xFFFF.

tests/lib/convert/unicode_tests.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.
 
 library unicode_tests;
 
 // Google favorite: "Îñţérñåţîöñåļîžåţîờñ".
 const INTER_BYTES = const [0xc3, 0x8e, 0xc3, 0xb1, 0xc5, 0xa3, 0xc3, 0xa9, 0x72,
                            0xc3, 0xb1, 0xc3, 0xa5, 0xc5, 0xa3, 0xc3, 0xae, 0xc3,
                            0xb6, 0xc3, 0xb1, 0xc3, 0xa5, 0xc4, 0xbc, 0xc3, 0xae,
@@ skipping 45 matching lines @@
 
 const SMALLEST_3_UTF8_UNIT_BYTES = const [ 0xE0, 0xA0, 0x80 ];
 const SMALLEST_3_UTF8_UNIT_STRING = "\u{800}";
 
 const BIGGEST_3_UTF8_UNIT_BYTES = const [ 0xEF, 0xBF, 0xBF ];
 const BIGGEST_3_UTF8_UNIT_STRING = "\u{FFFF}";
 
 const SMALLEST_4_UTF8_UNIT_BYTES = const [ 0xF0, 0x90, 0x80, 0x80 ];
 const SMALLEST_4_UTF8_UNIT_STRING = "\u{10000}";
 
+const BIGGEST_4_UTF8_UNIT_BYTES = const [ 0xF4, 0x8F, 0xBF, 0xBF ];
+const BIGGEST_4_UTF8_UNIT_STRING = "\u{10FFFF}";
+
 const _TEST_PAIRS = const [
     const [ const [], "" ],
     const [ INTER_BYTES, INTER_STRING ],
     const [ BLUEBERRY_BYTES, BLUEBERRY_STRING ],
     const [ SIVA_BYTES1, SIVA_STRING1 ],
     const [ SIVA_BYTES2, SIVA_STRING2 ],
     const [ BEE_BYTES, BEE_STRING ],
     const [ DIGIT_BYTES, DIGIT_STRING ],
     const [ ASCII_BYTES, ASCII_STRING ],
     const [ BIGGEST_ASCII_BYTES, BIGGEST_ASCII_STRING ],
     const [ SMALLEST_2_UTF8_UNIT_BYTES, SMALLEST_2_UTF8_UNIT_STRING ],
     const [ BIGGEST_2_UTF8_UNIT_BYTES, BIGGEST_2_UTF8_UNIT_STRING ],
     const [ SMALLEST_3_UTF8_UNIT_BYTES, SMALLEST_3_UTF8_UNIT_STRING ],
     const [ BIGGEST_3_UTF8_UNIT_BYTES, BIGGEST_3_UTF8_UNIT_STRING ],
     const [ SMALLEST_4_UTF8_UNIT_BYTES, SMALLEST_4_UTF8_UNIT_STRING ],
+    const [ BIGGEST_4_UTF8_UNIT_BYTES, BIGGEST_4_UTF8_UNIT_STRING ],
     ];
 
 List<List> _expandTestPairs() {
   assert(2 == BEE_STRING.length);
   var tests = [];
   tests.addAll(_TEST_PAIRS);
   tests.addAll(_TEST_PAIRS.expand((test) {
     var bytes = test[0];
     var string = test[1];
     var longBytes = [];
     var longString = "";
     for (int i = 0; i < 100; i++) {
       longBytes.addAll(bytes);
       longString += string;
     }
     return [test, [longBytes, longString]];
   }));
   return tests;
 }
 
 final List UNICODE_TESTS = _expandTestPairs();