Scrolling allowed when overflow:hidden (seen on Acid2)

Source/core/rendering/RenderBox.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2005, 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Adobe Systems Incorporated. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 735 matching lines @@
 }
 
 bool RenderBox::autoscrollInProgress() const
 {
     return frame() && frame()->page() && frame()->page()->autoscrollInProgress(this);
 }
 
 // There are two kinds of renderer that can autoscroll.
 bool RenderBox::canAutoscroll() const
 {
+    if (node() && node()->isDocumentNode())
+        return view()->frameView()->isScrollable();
+
     // Check for a box that can be scrolled in its own right.
-    if (canBeScrolledAndHasScrollableArea())
-        return true;
-
-    // Check for a box that represents the top level of a web page.
-    if (node() != &document())
-        return false;
-    Frame* frame = this->frame();
-    if (!frame)
-        return false;
-    Page* page = frame->page();
-    return page && page->mainFrame() == frame && frame->view()->isScrollable();
+    return canBeScrolledAndHasScrollableArea();
 }
 
 // If specified point is in border belt, returned offset denotes direction of
 // scrolling.
 IntSize RenderBox::calculateAutoscrollDirection(const IntPoint& windowPoint) const
 {
     if (!frame())
         return IntSize();
 
     FrameView* frameView = frame()->view();
@@ skipping 3932 matching lines @@
     }
 
     if (didSplitParentAnonymousBoxes)
         markBoxForRelayoutAfterSplit(this);
 
     ASSERT(beforeChild->parent() == this);
     return beforeChild;
 }
 
 } // namespace WebCore