Don't adjust for scrolling of the ancestor, rather than un-adjusting for it later.

third_party/WebKit/Source/core/layout/LayoutBox.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 995 matching lines @@
     if (isHorizontalWritingMode() && shouldPlaceBlockDirectionScrollbarOnLogicalLeft())
         result.expand(-verticalScrollbarWidth(), 0);
     return result;
 }
 
 bool LayoutBox::mapScrollingContentsRectToBoxSpace(LayoutRect& rect, ApplyOverflowClipFlag applyOverflowClip, VisualRectFlags visualRectFlags) const
 {
     if (!hasOverflowClip())
         return true;
 
+    if (applyOverflowClip == ApplyNonScrollOverflowClip && scrollsOverflow()) {
+        return true;
+    }
+
     LayoutSize offset = LayoutSize(-scrolledContentOffset());
     rect.move(offset);
 
-    if (applyOverflowClip == ApplyNonScrollOverflowClip && scrollsOverflow())
-        return true;
-
     LayoutRect clipRect = overflowClipRect(LayoutPoint());
 
     bool doesIntersect;
     if (visualRectFlags & EdgeInclusive) {
         doesIntersect = rect.inclusiveIntersect(clipRect);
     } else {
         rect.intersect(clipRect);
         doesIntersect = !rect.isEmpty();
     }
     return doesIntersect;
@@ skipping 3933 matching lines @@
         m_rareData->m_snapAreas->remove(&snapArea);
     }
 }
 
 SnapAreaSet* LayoutBox::snapAreas() const
 {
     return m_rareData ? m_rareData->m_snapAreas.get() : nullptr;
 }
 
 } // namespace blink