Paint solid color and local attachment backgrounds into scrolling 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 c0818175026a76d87c86744541c6ad4b8ad425d8..e80a003d02f94cb49fb7d58cc62fac133a86ee97 100644
--- a/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
+++ b/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
@@ -309,8 +309,16 @@ 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.
-        m_graphicsLayer->setContentsOpaque(m_owningLayer.backgroundIsKnownToBeOpaqueInRect(compositedBounds()));
+        const bool backgroundOpaque = m_owningLayer.backgroundIsKnownToBeOpaqueInRect(compositedBounds());
+        // Whether or not the background is painted into the primary graphics layer, it will be
+        // entirely occluded by an opaque background.
+        m_graphicsLayer->setContentsOpaque(backgroundOpaque);
+
+        // For non-root layers, background is painted by the scrolling contents layer if all backgrounds
+        // are solid color or background attachment local, otherwise background is painted by
+        // the primary graphics layer.
+        if (hasScrollingLayer() && m_owningLayer.shouldPaintBackgroundOntoForeground())
+            m_scrollingContentsLayer->setContentsOpaque(backgroundOpaque);
     }
 }