Fix Compositing of Opaque Scrolling Layers and Add Tests

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

Index: third_party/WebKit/Source/core/paint/PaintLayer.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayer.cpp b/third_party/WebKit/Source/core/paint/PaintLayer.cpp
index 9fa0a8e32d6fdd95aeccbb84c1e4ee9423d139bb..fcb7fc19646cbd5a55d195b375ec71fc52a1b7d3 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayer.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayer.cpp
@@ -2334,6 +2334,19 @@ GraphicsLayer* PaintLayer::graphicsLayerBackingForScrolling() const
     }
 }
 
+bool PaintLayer::shouldPaintBackgroundOntoScrollingContentsLayer() const
+{
+    // TODO(flackr): Add support for painting locally attached background images. https://crbug.com/625882
+    const FillLayer& backgroundLayer = layoutObject()->style()->backgroundLayers();
+    return !isRootLayer()
+        && scrollsOverflow()
+        && !backgroundLayer.image()
+        && !backgroundLayer.next()
+        && (backgroundLayer.attachment() == LocalBackgroundAttachment
+            || backgroundLayer.clip() == PaddingFillBox)
+        && !stackingNode()->hasNegativeZOrderList();
+}
+
 void PaintLayer::ensureCompositedLayerMapping()
 {
     if (m_rareData && m_rareData->compositedLayerMapping)