Fix unscrollable scrollers after closing a <dialog>.

third_party/WebKit/Source/core/dom/Document.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2011, 2012 Apple Inc. All
  * rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved.
  * (http://www.torchmobile.com/)
  * Copyright (C) 2008, 2009, 2011, 2012 Google Inc. All rights reserved.
@@ skipping 5628 matching lines @@
   element->setIsInTopLayer(true);
 }
 
 void Document::removeFromTopLayer(Element* element) {
   if (!element->isInTopLayer())
     return;
   size_t position = m_topLayerElements.find(element);
   DCHECK_NE(position, kNotFound);
   m_topLayerElements.remove(position);
   element->setIsInTopLayer(false);
+
+  // Any scrollers that were laid out from addToTopLayer need to be laid out
+  // again now to keep FrameView::m_scrollableAreas up to date. To that end,
+  // force normal layout instead of simplified layout on the document.
+  // See crbug.com/633520 for details.
+  if (layoutView())
+    layoutView()->setNeedsLayout(LayoutInvalidationReason::TopLayerChanged);
 }
 
 HTMLDialogElement* Document::activeModalDialog() const {
   if (m_topLayerElements.isEmpty())
     return 0;
   return toHTMLDialogElement(m_topLayerElements.last().get());
 }
 
 void Document::exitPointerLock() {
   if (!page())
@@ skipping 738 matching lines @@
 }
 
 void showLiveDocumentInstances() {
   WeakDocumentSet& set = liveDocumentSet();
   fprintf(stderr, "There are %u documents currently alive:\n", set.size());
   for (Document* document : set)
     fprintf(stderr, "- Document %p URL: %s\n", document,
             document->url().getString().utf8().data());
 }
 #endif