Expand PaintLayer clip to account for hidden URL bar with document.rootScroller

third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp

 /*
  * Copyright (C) 2009, 2010, 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 1289 matching lines @@
 void CompositedLayerMapping::updateScrollingLayerGeometry(
     const IntRect& localCompositingBounds) {
   if (!m_scrollingLayer)
     return;
 
   ASSERT(m_scrollingContentsLayer);
   LayoutBox* layoutBox = toLayoutBox(layoutObject());
   IntRect overflowClipRect =
       pixelSnappedIntRect(layoutBox->overflowClipRect(LayoutPoint()));
 
-  const TopDocumentRootScrollerController& globalRootScrollerController =
-      layoutBox->document().frameHost()->globalRootScrollerController();
-
-  if (&m_owningLayer == globalRootScrollerController.rootScrollerPaintLayer()) {
-    LayoutRect clipRect =
-        layoutBox->document().layoutView()->overflowClipRect(LayoutPoint());

[chrishtr, 2017/01/21 02:06:47]

Why can this now be removed?

-    DCHECK(clipRect.size() == LayoutSize(pixelSnappedIntRect(clipRect).size()));
-    overflowClipRect.setSize(pixelSnappedIntRect(clipRect).size());
-  }
-
   // When a m_childTransformLayer exists, local content offsets for the
   // m_scrollingLayer have already been applied. Otherwise, we apply them here.
   IntSize localContentOffset(0, 0);
   if (!m_childTransformLayer) {
     localContentOffset = roundedIntPoint(m_owningLayer.subpixelAccumulation()) -
                          localCompositingBounds.location();
   }
   m_scrollingLayer->setPosition(
       FloatPoint(overflowClipRect.location() + localContentOffset));
   m_scrollingLayer->setSize(FloatSize(overflowClipRect.size()));
@@ skipping 2114 matching lines @@
   } else if (graphicsLayer == m_decorationOutlineLayer.get()) {
     name = "Decoration Layer";
   } else {
     ASSERT_NOT_REACHED();
   }
 
   return name;
 }
 
 }  // namespace blink