Paint local attachment backgrounds into composited scrolling contents layer

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

Index: third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
diff --git a/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp b/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
index 51159637bc5b210ce7b76982670cd289db156338..8fe11b28904612a0a199ccd50186800033ecc019 100644
--- a/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
+++ b/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
@@ -309,7 +309,15 @@ void CompositedLayerMapping::updateContentsOpaque()
         m_graphicsLayer->setContentsOpaque(false);
         m_backgroundLayer->setContentsOpaque(m_owningLayer.backgroundIsKnownToBeOpaqueInRect(compositedBounds()));
     } else {
-        // For non-root layers, background is always painted by the primary graphics layer.
+        // For non-root layers, background is painted by the scrolling contents layer if all backgrounds
+        // are background attachment local, otherwise background is painted by the primary graphics layer.
+        if (hasScrollingLayer() && m_owningLayer.shouldPaintBackgroundOntoForeground()) {
+            // Backgrounds painted onto the foreground are clipped by the padding box rect.
+            // TODO(flackr): Check the entire overflow rect.
+            m_scrollingContentsLayer->setContentsOpaque(m_owningLayer.backgroundIsKnownToBeOpaqueInRect(toLayoutBox(layoutObject())->paddingBoxRect()));
+        }
+        // The border is always painted by the m_graphicsLayer, so we check if it is known to be
+        // opaque separately.
         m_graphicsLayer->setContentsOpaque(m_owningLayer.backgroundIsKnownToBeOpaqueInRect(compositedBounds()));
     }
 }
@@ -2421,8 +2429,11 @@ void CompositedLayerMapping::paintContents(const GraphicsLayer* graphicsLayer, G
         paintLayerFlags |= PaintLayerPaintingChildClippingMaskPhase;
     if (graphicsLayerPaintingPhase & GraphicsLayerPaintOverflowContents)
         paintLayerFlags |= PaintLayerPaintingOverflowContents;
-    if (graphicsLayerPaintingPhase & GraphicsLayerPaintCompositedScroll)
+    if (graphicsLayerPaintingPhase & GraphicsLayerPaintCompositedScroll) {
         paintLayerFlags |= PaintLayerPaintingCompositingScrollingPhase;
+        if (m_owningLayer.shouldPaintBackgroundOntoForeground())
+            paintLayerFlags |= PaintLayerPaintingBackgroundOntoForeground;
+    }
 
     if (graphicsLayer == m_backgroundLayer.get())
         paintLayerFlags |= (PaintLayerPaintingRootBackgroundOnly | PaintLayerPaintingCompositingForegroundPhase); // Need PaintLayerPaintingCompositingForegroundPhase to walk child layers.