Added offset document measurement to Element.

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 906 matching lines @@
   @Experimental()
   bool get isTemplate => tagName == 'TEMPLATE' || _isAttributeTemplate;
 
   void _ensureTemplate() {
     if (!isTemplate) {
       throw new UnsupportedError('$this is not a template.');
     }
     TemplateElement.decorate(this);
   }
 
+  /** Provides the coordinates of the element relative to the document. */
+  Point get documentOffset() {
+    final docElem = document.documentElement;
+    final box = getBoundingClientRect();
+    return new Point(box.left + window.pageXOffset - docElem.clientLeft,
+                     box.top + window.pageYOffset - docElem.clientTop);
+  }
 $!MEMBERS
 }
 
 
 final _START_TAG_REGEXP = new RegExp('<(\\w+)');
 class _ElementFactoryProvider {
   static const _CUSTOM_PARENT_TAG_MAP = const {
     'body' : 'html',
     'head' : 'html',
     'caption' : 'table',
@@ skipping 127 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');
 }