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

third_party/WebKit/Source/core/frame/FrameView.cpp

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999 Lars Knoll <knoll@kde.org>
  *                     1999 Antti Koivisto <koivisto@kde.org>
  *                     2000 Dirk Mueller <mueller@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *           (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
@@ skipping 2173 matching lines @@
 
         toLayoutCounter(layoutObject)->updateCounter();
     }
 }
 
 IntRect FrameView::windowClipRect(IncludeScrollbarsInRect scrollbarInclusion) const
 {
     ASSERT(m_frame->view() == this);
 
     LayoutRect clipRect(LayoutPoint(), LayoutSize(visibleContentSize(scrollbarInclusion)));
-    layoutViewItem().mapToVisualRectInAncestorSpace(&layoutView()->containerForPaintInvalidation(), clipRect);
+    const LayoutBoxModelObject* paintInvalidationContainer = &layoutView()->containerForPaintInvalidation();
+    layoutViewItem().mapToVisualRectInAncestorSpace(paintInvalidationContainer, clipRect);
+    if (paintInvalidationContainer->isBox()) {
+        const LayoutBox* box = toLayoutBox(paintInvalidationContainer);
+        if (box->hasOverflowClip())
+            clipRect.move(-box->scrolledContentOffset());
+    }
     return enclosingIntRect(clipRect);
 }
 
 bool FrameView::shouldUseIntegerScrollOffset() const
 {
     if (m_frame->settings() && !m_frame->settings()->preferCompositingToLCDTextEnabled())
         return true;
 
     return ScrollableArea::shouldUseIntegerScrollOffset();
 }
@@ skipping 2076 matching lines @@
 }
 
 bool FrameView::canThrottleRendering() const
 {
     if (!RuntimeEnabledFeatures::renderingPipelineThrottlingEnabled())
         return false;
     return m_subtreeThrottled || (m_hiddenForThrottling && m_crossOriginForThrottling);
 }
 
 } // namespace blink