overflow-y: hidden areas can still be scrolled vertically

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 713 matching lines @@
     return false;
 }
 
 bool RenderBox::canBeScrolledAndHasScrollableArea() const
 {
     return canBeProgramaticallyScrolled() && (scrollHeight() != clientHeight() || scrollWidth() != clientWidth());
 }
 
 bool RenderBox::canBeProgramaticallyScrolled() const
 {
-    return (hasOverflowClip() && (scrollsOverflow() || (node() && node()->rendererIsEditable()))) || (node() && node()->isDocumentNode());
+    Node* node = this->node();
+    if (node && node->isDocumentNode())
+        return true;
+
+    if (!hasOverflowClip())
+        return false;
+
+    bool hasScrollableOverflow = hasScrollableOverflowX() || hasScrollableOverflowY();
+    if (scrollsOverflow() && hasScrollableOverflow)
+        return true;
+
+    return node && node->rendererIsEditable();
 }
 
 bool RenderBox::usesCompositedScrolling() const
 {
     return hasOverflowClip() && hasLayer() && layer()->usesCompositedScrolling();
 }
 
 void RenderBox::autoscroll(const IntPoint& position)
 {
     if (layer())
@@ skipping 3965 matching lines @@
     }
 
     if (didSplitParentAnonymousBoxes)
         markBoxForRelayoutAfterSplit(this);
 
     ASSERT(beforeChild->parent() == this);
     return beforeChild;
 }
 
 } // namespace WebCore