Implementing CustomElement's attributeChanged callback.

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> {
   // Raw Element.
   final Element _element;
   final HtmlCollection _childElements;
@@ skipping 703 matching lines @@
   @Experimental()
   void enteredView() {}
 
   /**
    * Called by the DOM when this element has been removed from the live
    * document.
    */
   @Experimental()
   void leftView() {}
 
+  /**
+   * Called by the DOM whenever an attribute on this has been changed.
+   */
+  void attributeChanged(String name, String oldValue, String newValue) {}
+
   // Hooks to support custom WebComponents.
 
 $if DART2JS
   @Creates('Null')  // Set from Dart code; does not instantiate a native type.
 $endif
   Element _xtag;
 
   /**
    * Experimental support for [web components][wc]. This field stores a
    * reference to the component implementation. It was inspired by Mozilla's
@@ skipping 660 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');
 }