Revert "Remove deprecated mappedBy."

sdk/lib/html/html_common/filtered_element_list.dart

 // Copyright (c) 2011, 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_common;
 
 /**
  * An indexable collection of a node's descendants in the document tree,
  * filtered so that only elements are in the collection.
  */
@@ skipping 84 matching lines @@
 
   Element removeLast() {
     final result = this.last;
     if (result != null) {
       result.remove();
     }
     return result;
   }
 
   Iterable map(f(Element element)) => _filtered.map(f);
+  List mappedBy(f(Element element)) => _filtered.mappedBy(f);
   Iterable<Element> where(bool f(Element element)) => _filtered.where(f);
   Iterable expand(Iterable f(Element element)) => _filtered.expand(f);
 
   Element removeAt(int index) {
     final result = this[index];
     result.remove();
     return result;
   }
 
   void remove(Object element) {
@@ skipping 83 matching lines @@
   Element get first => _filtered.first;
 
   Element get last => _filtered.last;
 
   Element get single => _filtered.single;
 
   Element min([int compare(Element a, Element b)]) => _filtered.min(compare);
 
   Element max([int compare(Element a, Element b)]) => _filtered.max(compare);
 }