Show a vertical scrollbar (when needed) for overflow:-webkit-paged-y.

Source/core/rendering/RenderBox.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2003, 2006, 2007 Apple Inc. 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
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 468 matching lines @@
     virtual bool scroll(ScrollDirection, ScrollGranularity, float delta = 1);
     bool canBeScrolledAndHasScrollableArea() const;
     virtual bool canBeProgramaticallyScrolled() const;
     virtual void autoscroll(const IntPoint&);
     bool canAutoscroll() const;
     IntSize calculateAutoscrollDirection(const IntPoint& windowPoint) const;
     static RenderBox* findAutoscrollable(LayoutObject*);
     virtual void stopAutoscroll() { }
     virtual void panScroll(const IntPoint&);
 
-    bool hasAutoVerticalScrollbar() const { return hasOverflowClip() && (style()->overflowY() == OAUTO || style()->overflowY() == OOVERLAY); }
+    bool hasAutoVerticalScrollbar() const { return hasOverflowClip() && (style()->overflowY() == OAUTO || style()->overflowY() == OPAGEDY || style()->overflowY() == OOVERLAY); }
     bool hasAutoHorizontalScrollbar() const { return hasOverflowClip() && (style()->overflowX() == OAUTO || style()->overflowX() == OOVERLAY); }
     bool scrollsOverflow() const { return scrollsOverflowX() || scrollsOverflowY(); }
 
     bool hasScrollableOverflowX() const { return scrollsOverflowX() && pixelSnappedScrollWidth() != pixelSnappedClientWidth(); }
     bool hasScrollableOverflowY() const { return scrollsOverflowY() && pixelSnappedScrollHeight() != pixelSnappedClientHeight(); }
     virtual bool scrollsOverflowX() const { return hasOverflowClip() && (style()->overflowX() == OSCROLL || hasAutoHorizontalScrollbar()); }
     virtual bool scrollsOverflowY() const { return hasOverflowClip() && (style()->overflowY() == OSCROLL || hasAutoVerticalScrollbar()); }
     bool usesCompositedScrolling() const;
 
     // Elements such as the <input> field override this to specify that they are scrollable
@@ skipping 343 matching lines @@
         if (UNLIKELY(inlineBoxWrapper() != 0))
             deleteLineBoxWrapper();
     }
 
     ensureRareData().m_inlineBoxWrapper = boxWrapper;
 }
 
 } // namespace blink
 
 #endif // RenderBox_h