Record box shadow as main thread scrolling reasons

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 73e6debb93a0f95c56cb0ae8c10362ba4c388675..df0853754cf2c3a6f372da38e7224de44f521584 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayer.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayer.cpp
@@ -2609,11 +2609,12 @@ GraphicsLayer* PaintLayer::graphicsLayerBacking(const LayoutObject* obj) const {
   }
 }
 
-BackgroundPaintLocation PaintLayer::backgroundPaintLocation() const {
+BackgroundPaintLocation PaintLayer::backgroundPaintLocation(
+    uint32_t* reasons) const {
   BackgroundPaintLocation location =
       isRootLayer() || !scrollsOverflow()
           ? BackgroundPaintInGraphicsLayer
-          : layoutObject()->backgroundPaintLocation();
+          : layoutObject()->backgroundPaintLocation(reasons);
   m_stackingNode->updateLayerListsIfNeeded();
   if (m_stackingNode->hasNegativeZOrderList())
     location = BackgroundPaintInGraphicsLayer;