<picture>: Update the <img> element when a <source> changes

Source/core/html/HTMLPictureElement.cpp

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 #include "core/html/HTMLPictureElement.h"
 
 #include "HTMLNames.h"
+#include "core/dom/ElementTraversal.h"
+#include "core/html/HTMLImageElement.h"
 
 namespace WebCore {
 
 using namespace HTMLNames;
 
 HTMLPictureElement::HTMLPictureElement(Document& document)
     : HTMLElement(pictureTag, document)
 {
     ScriptWrappable::init(this);
 }
 
+void HTMLPictureElement::sourceOrMediaChanged()
+{
+    for (HTMLImageElement* imageElement = Traversal<HTMLImageElement>::firstChild(*this); imageElement; imageElement = Traversal<HTMLImageElement>::nextSibling(*imageElement)) {
+        imageElement->selectSourceURL(HTMLImageElement::UpdateNormal);
+    }
+}
+
 } // namespace