Remove Collection, Collections and clean up List/Set/Queue implementations of retain/remove.

tools/dom/src/CssClassSet.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 html;
 
 abstract class CssClassSet implements Set<String> {
 
   String toString() {
     return readClasses().join(' ');
@@ skipping 130 matching lines @@
   }
 
   void removeWhere(bool test(String name)) {
     _modify((s) => s.removeWhere(test));
   }
 
   void retainWhere(bool test(String name)) {
     _modify((s) => s.retainWhere(test));
   }
 
-  bool isSubsetOf(Collection<String> collection) =>
-    readClasses().isSubsetOf(collection);
-
   bool containsAll(Iterable<String> collection) =>
     readClasses().containsAll(collection);
 
   Set<String> intersection(Set<String> other) =>
     readClasses().intersection(other);
 
   Set<String> union(Set<String> other) =>
     readClasses().union(other);
 
   Set<String> difference(Set<String> other) =>
@@ skipping 46 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);
 }