Example showing alternate async measurement solution

client/html/src/DocumentFragmentWrappingImplementation.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.
 
 class FilteredElementList implements ElementList {
   final Node _node;
   final NodeList _childNodes;
 
   FilteredElementList(Node node): _childNodes = node.nodes, _node = node;
 
   // We can't memoize this, since it's possible that children will be messed
@@ skipping 112 matching lines @@
     throw new UnsupportedOperationException(
         "Can't modify a frozen style declaration.");
   }
 
   void setProperty(String propertyName, String value, [String priority]) {
     throw new UnsupportedOperationException(
         "Can't modify a frozen style declaration.");
   }
 }
 
-Future<CSSStyleDeclaration> _emptyStyleFuture() {
-  return _createMeasurementFuture(() => new EmptyStyleDeclaration(),
-                                  new Completer<CSSStyleDeclaration>());
-}
-
 class EmptyElementRect implements ElementRect {
   final ClientRect client = const SimpleClientRect(0, 0, 0, 0);
   final ClientRect offset = const SimpleClientRect(0, 0, 0, 0);
   final ClientRect scroll = const SimpleClientRect(0, 0, 0, 0);
   final ClientRect bounding = const SimpleClientRect(0, 0, 0, 0);
   final List<ClientRect> clientRects = const <ClientRect>[];
 
   const EmptyElementRect();
 }
 
@@ skipping 77 matching lines @@
       position_OR_where, new DocumentFragment.html(text));
   }
 
   ElementEvents get on() {
     if (_on === null) {
       _on = new ElementEventsImplementation._wrap(_ptr);
     }
     return _on;
   }
 
-  Future<ElementRect> get rect() {
-    return _createMeasurementFuture(() => const EmptyElementRect(),
-                                    new Completer<ElementRect>());
+  ElementRect get rect() {
+    // A document fragment can never be attached to a Document so it always
+    // safe to measure.
+    return const EmptyElementRect();
   }
 
   Element query(String selectors) =>
     LevelDom.wrapElement(_ptr.querySelector(selectors));
 
   ElementList queryAll(String selectors) =>
     LevelDom.wrapElementList(_ptr.querySelectorAll(selectors));
 
   // If we can come up with a semi-reasonable default value for an Element
   // getter, we'll use it. In general, these return the same values as an
@@ skipping 12 matching lines @@
   Element get lastElementChild() => elements.last();
   Element get nextElementSibling() => null;
   Element get previousElementSibling() => null;
   Element get offsetParent() => null;
   Element get parent() => null;
   Map<String, String> get attributes() => const {};
   // Issue 174: this should be a const set.
   Set<String> get classes() => new Set<String>();
   Map<String, String> get dataAttributes() => const {};
   CSSStyleDeclaration get style() => new EmptyStyleDeclaration();
-  Future<CSSStyleDeclaration> get computedStyle() =>
-      _emptyStyleFuture();
-  Future<CSSStyleDeclaration> getComputedStyle(String pseudoElement) =>
-      _emptyStyleFuture();
+  CSSStyleDeclaration get computedStyle() => new EmptyStyleDeclaration();
+  CSSStyleDeclaration getComputedStyle(String pseudoElement) =>
+      new EmptyStyleDeclaration();
   bool matchesSelector([String selectors]) => false;
 
   // Imperative Element methods are made into no-ops, as they are on parentless
   // elements.
   void blur() {}
   void focus() {}
   void scrollByLines([int lines]) {}
   void scrollByPages([int pages]) {}
   void scrollIntoView([bool centerIfNeeded]) {}
 
@@ skipping 79 matching lines @@
       "Title can't be set for document fragments.");
   }
 
   void set webkitdropzone(String value) {
     throw new UnsupportedOperationException(
       "WebKit drop zone can't be set for document fragments.");
   }
 
   DocumentFragment clone(bool deep) => super.clone(deep);
 }