Added expand method to iterables.

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;
 
 // TODO(jacobr): use _Lists.dart to remove some of the duplicated
 // functionality.
 class _ChildrenElementList implements List {
   // Raw Element.
@@ skipping 55 matching lines @@
   }
 
   List mappedBy(f(Element element)) {
     return IterableMixinWorkaround.mappedByList(this, f);
   }
 
   Iterable<Element> where(bool f(Element element)) {
     return IterableMixinWorkaround.where(this, f);
   }
 
+  Iterable expand(Iterable f(Element element)) {
+    return IterableMixinWorkaround.expand(this, f);
+  }
+
   bool get isEmpty {
     return _element.$dom_firstElementChild == null;
   }
 
   Iterable<Element> take(int n) {
     return IterableMixinWorkaround.takeList(this, n);
   }
 
   Iterable<Element> takeWhile(bool test(Element value)) {
     return IterableMixinWorkaround.takeWhile(this, test);
@@ skipping 197 matching lines @@
   }
 
   List mappedBy(f(Element element)) {
     return IterableMixinWorkaround.mappedByList(this, f);
   }
 
   Iterable<Element> where(bool f(Element element)) {
     return IterableMixinWorkaround.where(this, f);
   }
 
+  Iterable expand(Iterable f(Element element)) {
+    return IterableMixinWorkaround.expand(this, f);
+  }
+
   bool every(bool f(Element element)) {
     for(Element element in this) {
       if (!f(element)) {
         return false;
       }
     };
     return true;
   }
 
   bool any(bool f(Element element)) {
@@ skipping 724 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
 }