Add type annotations to some dart:html closures

tools/dom/templates/html/impl/impl_Element.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;
 
 class _ChildrenElementList extends ListBase<Element>
     implements NodeListWrapper {
   // Raw Element.
   final Element _element;
@@ skipping 279 matching lines @@
   Element get last => _nodeList.last;
 
   Element get single => _nodeList.single;
 
   CssClassSet get classes => new _MultiElementCssClassSet(this);
 
   CssStyleDeclarationBase get style =>
       new _CssStyleDeclarationSet(this);
 
   void set classes(Iterable<String> value) {
+    // TODO(sra): This might be faster for Sets:
+    //
+    //     new _MultiElementCssClassSet(this).writeClasses(value)
+    //
+    // as the code below converts the Iterable[value] to a string multiple
+    // times.  Maybe
+
     _nodeList.forEach((e) => e.classes = value);
   }
 
   CssRect get contentEdge => new _ContentCssListRect(this);
 
   CssRect get paddingEdge => this.first.paddingEdge;
 
   CssRect get borderEdge => this.first.borderEdge;
 
   CssRect get marginEdge => this.first.marginEdge;
@@ skipping 306 matching lines @@
    * This set makes it easy to add, remove or toggle the classes applied to
    * this element.
    *
    *     element.classes.add('selected');
    *     element.classes.toggle('isOnline');
    *     element.classes.remove('selected');
    */
   CssClassSet get classes => new _ElementCssClassSet(this);
 
   void set classes(Iterable<String> value) {
+    // TODO(sra): Do this without reading the classes in clear() and addAll(),
+    // or writing the classes in clear().
     CssClassSet classSet = classes;
     classSet.clear();
     classSet.addAll(value);
   }
 
   /**
    * Allows access to all custom data attributes (data-*) set on this element.
    *
    * The keys for the map must follow these rules:
    *
@@ skipping 844 matching lines @@
   const ScrollAlignment._internal(this._value);
   toString() => 'ScrollAlignment.$_value';
 
   /// Attempt to align the element to the top of the scrollable area.
   static const TOP = const ScrollAlignment._internal('TOP');
   /// Attempt to center the element in the scrollable area.
   static const CENTER = const ScrollAlignment._internal('CENTER');
   /// Attempt to align the element to the bottom of the scrollable area.
   static const BOTTOM = const ScrollAlignment._internal('BOTTOM');
 }