Fix unscrollable scrollers after closing a <dialog>.

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

Index: third_party/WebKit/Source/core/dom/Document.cpp
diff --git a/third_party/WebKit/Source/core/dom/Document.cpp b/third_party/WebKit/Source/core/dom/Document.cpp
index 88e8ddba1d5c4b64bf97c45c03775722e611459a..8b28babed7e89b01c541aca486a53c51d50d2890 100644
--- a/third_party/WebKit/Source/core/dom/Document.cpp
+++ b/third_party/WebKit/Source/core/dom/Document.cpp
@@ -5646,6 +5646,13 @@ void Document::removeFromTopLayer(Element* 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 {