Move Point and Rect over to dart:math, to be re-exported by dart:html.

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 624 matching lines @@
     if (pseudoElement == null) {
       pseudoElement = '';
     }
     // TODO(jacobr): last param should be null, see b/5045788
     return window._getComputedStyle(this, pseudoElement);
   }
 
   /**
    * Gets the position of this element relative to the client area of the page.
    */
-  Rect get client => new Rect(clientLeft, clientTop, clientWidth, clientHeight);
+  Rectangle get client => new Rectangle(clientLeft, clientTop, clientWidth, 
+      clientHeight);
 
   /**
    * Gets the offset of this element relative to its offsetParent.
    */
-  Rect get offset => new Rect(offsetLeft, offsetTop, offsetWidth, offsetHeight);
+  Rectangle get offset => new Rectangle(offsetLeft, offsetTop, offsetWidth, 
+      offsetHeight);
 
   /**
    * Adds the specified text after the last child of this element.
    */
   void appendText(String text) {
     this.insertAdjacentText('beforeend', text);
   }
 
   /**
    * Parses the specified text as HTML and adds the resulting node after the
@@ skipping 706 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');
 }