Paint local background colors onto foreground layer.

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

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/paint/PaintLayerPainter.h"
 
 #include "core/frame/FrameView.h"
 #include "core/frame/Settings.h"
 #include "core/layout/LayoutBlock.h"
 #include "core/layout/LayoutView.h"
@@ skipping 363 matching lines @@
             ASSERT(objectPaintProperties && objectPaintProperties->localBorderBoxProperties());
             PaintChunkProperties properties(context.getPaintController().currentPaintChunkProperties());
             auto& localBorderBoxProperties = *objectPaintProperties->localBorderBoxProperties();
             properties.transform = localBorderBoxProperties.propertyTreeState.transform;
             properties.clip = localBorderBoxProperties.propertyTreeState.clip;
             properties.effect = localBorderBoxProperties.propertyTreeState.effect;
             properties.backfaceHidden = m_paintLayer.layoutObject()->hasHiddenBackface();
             scopedPaintChunkProperties.emplace(context.getPaintController(), m_paintLayer, properties);
         }
 
-        bool shouldPaintBackground = isPaintingCompositedBackground && shouldPaintContent && !selectionOnly;
+        bool shouldPaintBackgroundOntoForeground = paintFlags & PaintLayerPaintingCompositingScrollingPhase
+            && m_paintLayer.shouldPaintBackgroundOntoForeground();
+        bool shouldPaintBackground = shouldPaintContent && !selectionOnly
+            && (shouldPaintBackgroundOntoForeground || isPaintingCompositedBackground);
         bool shouldPaintNegZOrderList = (isPaintingScrollingContent && isPaintingOverflowContents) || (!isPaintingScrollingContent && isPaintingCompositedBackground);
         bool shouldPaintOwnContents = isPaintingCompositedForeground && shouldPaintContent;
         bool shouldPaintNormalFlowAndPosZOrderLists = isPaintingCompositedForeground;
         bool shouldPaintOverlayScrollbars = isPaintingOverlayScrollbars;
 
         if (shouldPaintBackground) {
+            PaintLayerFlags localPaintFlags(paintFlags);
+            if (shouldPaintBackgroundOntoForeground)
+                localPaintFlags |= PaintLayerPaintingRootBackgroundOntoForeground;
             paintBackgroundForFragments(layerFragments, context, paintingInfo.paintDirtyRect,
-                localPaintingInfo, paintFlags);
+                localPaintingInfo, localPaintFlags);
         }
 
         if (shouldPaintNegZOrderList) {
             if (paintChildren(NegativeZOrderChildren, context, paintingInfo, paintFlags) == MayBeClippedByPaintDirtyRect)
                 result = MayBeClippedByPaintDirtyRect;
         }
 
         if (shouldPaintOwnContents) {
             paintForegroundForFragments(layerFragments, context, paintingInfo.paintDirtyRect,
                 localPaintingInfo, selectionOnly, paintFlags);
@@ skipping 406 matching lines @@
     if (!m_paintLayer.containsDirtyOverlayScrollbars())
         return;
 
     PaintLayerPaintingInfo paintingInfo(&m_paintLayer, LayoutRect(enclosingIntRect(damageRect)), paintFlags, LayoutSize());
     paintLayer(context, paintingInfo, PaintLayerPaintingOverlayScrollbars);
 
     m_paintLayer.setContainsDirtyOverlayScrollbars(false);
 }
 
 } // namespace blink