Fix for bug 18596- analyzer warning in dart:html under Dartium

tools/dom/src/native_DOMImplementation.dart

 // 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;
 
 class _ConsoleVariables {
   Map<String, Object> _data = new Map<String, Object>();
 
   /**
@@ skipping 399 matching lines @@
     _register(document, tag, type, extendsTagName);
   }
 
   static void _register(Document document, String tag, Type customType,
       String extendsTagName) native "Utils_register";
 
   static Element createElement(Document document, String tagName) native "Utils_createElement";
 
   static void initializeCustomElement(HtmlElement element) native "Utils_initializeCustomElement";
 
-  static void changeElementWrapper(HtmlElement element, Type type) native "Utils_changeElementWrapper";
+  static Element changeElementWrapper(HtmlElement element, Type type) native "Utils_changeElementWrapper";
 }
 
 class _DOMWindowCrossFrame extends NativeFieldWrapperClass2 implements
     WindowBase {
   _DOMWindowCrossFrame.internal();
 
   // Fields.
   HistoryBase get history native "Window_history_cross_frame_Getter";
   LocationBase get location native "Window_location_cross_frame_Getter";
   bool get closed native "Window_closed_Getter";
@@ skipping 165 matching lines @@
   _scheduleImmediateHelper._schedule(callback);
 };
 
 get _pureIsolateScheduleImmediateClosure => ((void callback()) =>
   throw new UnimplementedError("scheduleMicrotask in background isolates "
                                "are not supported in the browser"));
 
 void _initializeCustomElement(Element e) {
   _Utils.initializeCustomElement(e);
 }