Example showing alternate async measurement solution

client/html/src/Element.dart

-// Copyright (c) 2011, the Dart project authors.  Please see the AUTHORS file
+// 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.
 
 interface ElementList extends List<Element> {
   // TODO(jacobr): add element batch manipulation methods.
   Element get first();
   // TODO(jacobr): add insertAt
 }
 
-class DeferredElementRect {
-  // TODO(jacobr)
-}
-
 interface ElementEvents extends Events {
   EventListenerList get abort();
   EventListenerList get beforeCopy();
   EventListenerList get beforeCut();
   EventListenerList get beforePaste();
   EventListenerList get blur();
   EventListenerList get change();
   EventListenerList get click();
   EventListenerList get contextMenu();
   EventListenerList get copy();
@@ skipping 153 matching lines @@
   Element get parent();
 
   void scrollByLines([int lines]);
 
   void scrollByPages([int pages]);
 
   void scrollIntoView([bool centerIfNeeded]);
 
   bool matchesSelector([String selectors]);
 
-  Future<ElementRect> get rect();
+  /** Only access members when [window.inMeasurementFrame] is true. */
+  ElementRect get rect();
 
-  Future<CSSStyleDeclaration> get computedStyle();
+  /** Only call when [window.inMeasurementFrame] is true. */
+  CSSStyleDeclaration get computedStyle();
 
-  Future<CSSStyleDeclaration> getComputedStyle(String pseudoElement);
+  /** Only call when [window.inMeasurementFrame] is true. */
+  CSSStyleDeclaration getComputedStyle(String pseudoElement);
 
   ElementEvents get on();
 
   Element clone(bool deep);
 }