Revert "Remaining private libs"

sdk/lib/html/html_common/css_class_set.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.
 
-part of "dart:html_common";
+part of html_common;
 
 abstract class CssClassSetImpl implements CssClassSet {
   static final RegExp _validTokenRE = new RegExp(r'^\S+$');
 
   String _validateToken(String value) {
     if (_validTokenRE.hasMatch(value)) return value;
     throw new ArgumentError.value(value, 'value', 'Not a valid class token');
   }
 
   String toString() {
@@ skipping 217 matching lines @@
    */
   Set<String> readClasses();
 
   /**
    * Join all the elements of a set into one string and write
    * back to the element.
    * This is intended to be overridden by specific implementations.
    */
   void writeClasses(Set<String> s);
 }