Add Dart code to diff_view

pkg/compiler/lib/src/tokens/token.dart

 // Copyright (c) 2011, 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 dart2js.tokens;
 
 import 'dart:convert' show
     UTF8;
 import 'dart:collection' show
     HashSet;
@@ skipping 94 matching lines @@
   int get charCount {
     if (info == Precedence.BAD_INPUT_INFO) {
       // This is a token that wraps around an error message. Return 1
       // instead of the size of the length of the error message.
       return 1;
     } else {
       return value.length;
     }
   }
 
+  /// The character offset of the end of this token within the source text.
+  int get charEnd => charOffset + charCount;
+
   int get hashCode => computeHashCode(charOffset, info, value);
 }
 
 /// A pair of tokens marking the beginning and the end of a span. Use for error
 /// reporting.
 class TokenPair implements Spannable {
   final Token begin;
   final Token end;
 
   TokenPair(this.begin, this.end);
@@ skipping 306 matching lines @@
       (identical(value, '<=')) ||
       (identical(value, '<')) ||
       (identical(value, '&')) ||
       (identical(value, '^')) ||
       (identical(value, '|'));
 }
 
 bool isTernaryOperator(String value) => identical(value, '[]=');
 
 bool isMinusOperator(String value) => identical(value, '-');