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

tools/dom/templates/html/impl/impl_Storage.darttemplate

 // 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 $LIBRARYNAME;
 
 /**
  * The type used by the
  * [Window.localStorage] and [Window.sessionStorage] properties.
  * Storage is implemented as a Map<String, String>.
@@ skipping 45 matching lines @@
 
   void forEach(void f(String key, String value)) {
     for (var i = 0; true; i++) {
       final key = $dom_key(i);
       if (key == null) return;
 
       f(key, this[key]);
     }
   }
 
-  Collection<String> get keys {
+  Iterable<String> get keys {
     final keys = [];
     forEach((k, v) => keys.add(k));
     return keys;
   }
 
-  Collection<String> get values {
+  Iterable<String> get values {
     final values = [];
     forEach((k, v) => values.add(v));
     return values;
   }
 
   int get length => $dom_length;
 
   bool get isEmpty => $dom_key(0) == null;
 $!MEMBERS
 }