Changing window.requestLayoutFrame into a microtask API

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 html;
 
 // TODO(jacobr): use _Lists.dart to remove some of the duplicated
 // functionality.
 class _ChildrenElementList implements List {
   // Raw Element.
@@ skipping 689 matching lines @@
 
   /**
    * The set of all CSS values applied to this element, including inherited
    * and default values.
    *
    * The computedStyle contains values that are inherited from other
    * sources, such as parent elements or stylesheets. This differs from the
    * [style] property, which contains only the values specified directly on this
    * element.
    *
+   * PseudoElement can be values such as `::after`, `::before`, `::marker`,
+   * `::line-marker`.
+   *
    * See also:
    *
    * * [CSS Inheritance and Cascade](http://docs.webplatform.org/wiki/tutorials/inheritance_and_cascade)
+   * * [Pseudo-elements](http://docs.webplatform.org/wiki/css/selectors/pseudo-elements)
    */
-  Future<CssStyleDeclaration> get computedStyle {
-     // TODO(jacobr): last param should be null, see b/5045788
-     return getComputedStyle('');
+  CssStyleDeclaration getComputedStyle([String pseudoElement]) {
+    if (pseudoElement == null) {
+      pseudoElement = '';
+    }
+    // TODO(jacobr): last param should be null, see b/5045788
+    return window.$dom_getComputedStyle(this, pseudoElement);
   }
 
   /**
-   * Returns the computed styles for pseudo-elements such as `::after`,
-   * `::before`, `::marker`, `::line-marker`.
-   *
-   * See also:
-   *
-   * * [Pseudo-elements](http://docs.webplatform.org/wiki/css/selectors/pseudo-elements)
-   */
-  Future<CssStyleDeclaration> getComputedStyle(String pseudoElement) {
-    return _createMeasurementFuture(
-        () => window.$dom_getComputedStyle(this, pseudoElement),
-        new Completer<CssStyleDeclaration>());
-  }
-
-  /**
    * Adds the specified element to after the last child of this element.
    */
   void append(Element e) {
     this.children.add(e);
   }
 
   /**
    * Adds the specified text as a text node after the last child of this
    * element.
    */
@@ skipping 300 matching lines @@
 $if DART2JS
   // Optimization to improve performance until the dart2js compiler inlines this
   // method.
   static dynamic createElement_tag(String tag) =>
       JS('Element', 'document.createElement(#)', tag);
 $else
   static Element createElement_tag(String tag) =>
       document.$dom_createElement(tag);
 $endif
 }