Fix dartanalyzer issue with const

sdk/lib/html/dart2js/html_dart2js.dart

 library html;
 
 import 'dart:isolate';
 import 'dart:json';
 import 'dart:svg' as svg;
 import 'dart:web_audio' as web_audio;
 // 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.
 
@@ skipping 21932 matching lines @@
   /** The set of functions that wish to be notified when a KeyEvent happens. */
   List<Function> _callbacks;
 
   /** The type of KeyEvent we are tracking (keyup, keydown, keypress). */
   String _type;
 
   /** The element we are watching for events to happen on. */
   EventTarget _target;
 
   // The distance to shift from upper case alphabet Roman letters to lower case.
-  const int _ROMAN_ALPHABET_OFFSET = "a".charCodes[0] - "A".charCodes[0];
+  int _ROMAN_ALPHABET_OFFSET = "a".charCodes[0] - "A".charCodes[0];
 
   // Instance members referring to the internal event handlers because closures
   // are not hashable.
   var _keyUp, _keyDown, _keyPress;
 
   /**
    * An enumeration of key identifiers currently part of the W3C draft for DOM3
    * and their mappings to keyCodes.
    * http://www.w3.org/TR/DOM-Level-3-Events/keyset.html#KeySet-Set
    */
@@ skipping 3044 matching lines @@
     if (length < 0) throw new ArgumentError('length');
     if (start < 0) throw new RangeError.value(start);
     int end = start + length;
     if (end > a.length) throw new RangeError.value(end);
     for (int i = start; i < end; i++) {
       accumulator.add(a[i]);
     }
     return accumulator;
   }
 }