Paint solid color background into both scrolling contents layer and graphics layer.

third_party/WebKit/Source/core/paint/PaintLayer.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights
  * reserved.
  *
  * Portions are Copyright (C) 1998 Netscape Communications Corporation.
  *
  * Other contributors:
  *   Robert O'Callahan <roc+@cs.cmu.edu>
  *   David Baron <dbaron@fas.harvard.edu>
  *   Christian Biesinger <cbiesinger@web.de>
@@ skipping 2641 matching lines @@
       return 0;
     case PaintsIntoGroupedBacking:
       return groupedMapping()->squashingLayer();
     default:
       return compositedLayerMapping()->scrollingContentsLayer()
                  ? compositedLayerMapping()->scrollingContentsLayer()
                  : compositedLayerMapping()->mainGraphicsLayer();
   }
 }
 
-bool PaintLayer::canPaintBackgroundOntoScrollingContentsLayer() const {
-  if (isRootLayer() || !scrollsOverflow() ||
-      !layoutObject()->hasLocalEquivalentBackground())
-    return false;
-
+BackgroundPaintLocation PaintLayer::backgroundPaintLocation() const {
+  BackgroundPaintLocation location =
+      isRootLayer() || !scrollsOverflow()
+          ? BackgroundPaintInGraphicsLayer
+          : layoutObject()->backgroundPaintLocation();
   m_stackingNode->updateLayerListsIfNeeded();
-  return !m_stackingNode->hasNegativeZOrderList();
+  if (m_stackingNode->hasNegativeZOrderList())
+    location = BackgroundPaintInGraphicsLayer;
+  return location;
 }
 
 void PaintLayer::ensureCompositedLayerMapping() {
   if (m_rareData && m_rareData->compositedLayerMapping)
     return;
 
   ensureRareData().compositedLayerMapping =
       wrapUnique(new CompositedLayerMapping(*this));
   m_rareData->compositedLayerMapping->setNeedsGraphicsLayerUpdate(
       GraphicsLayerUpdateSubtree);
@@ skipping 590 matching lines @@
 }
 
 void showLayerTree(const blink::LayoutObject* layoutObject) {
   if (!layoutObject) {
     LOG(INFO) << "Cannot showLayerTree. Root is (nil)";
     return;
   }
   showLayerTree(layoutObject->enclosingLayer());
 }
 #endif