DeprecatedPaintLayerStackingNode should walk DPL

Source/core/paint/DeprecatedPaintLayer.cpp

Index: Source/core/paint/DeprecatedPaintLayer.cpp
diff --git a/Source/core/paint/DeprecatedPaintLayer.cpp b/Source/core/paint/DeprecatedPaintLayer.cpp
index ea5ca4adb958b53c529104ad7a03b529d764bc0b..12ca19260f7bfecb3a1c0267df1132d2d9e2bae4 100644
--- a/Source/core/paint/DeprecatedPaintLayer.cpp
+++ b/Source/core/paint/DeprecatedPaintLayer.cpp
@@ -1366,7 +1366,9 @@ void DeprecatedPaintLayer::updateStackingNode()
 {
     ASSERT(!m_stackingNode);
     if (requiresStackingNode())
-        m_stackingNode = adoptPtr(new DeprecatedPaintLayerStackingNode(*layoutObject()));
+        m_stackingNode = adoptPtr(new DeprecatedPaintLayerStackingNode(this));
+    else
+        m_stackingNode = nullptr;
 }
 
 void DeprecatedPaintLayer::updateScrollableArea()
@@ -1549,6 +1551,12 @@ Node* DeprecatedPaintLayer::enclosingElement() const
     return 0;
 }
 
+bool DeprecatedPaintLayer::isInTopLayer() const
+{
+    Node* node = layoutObject()->node();
+    return node && node->isElementNode() && toElement(node)->isInTopLayer();
+}
+
 // Compute the z-offset of the point in the transformState.
 // This is effectively projecting a ray normal to the plane of ancestor, finding where that
 // ray intersects target, and computing the z delta between those two points.