Compute style-determined compositing reasons during recalc style

Source/core/rendering/RenderLayer.h

Index: Source/core/rendering/RenderLayer.h
diff --git a/Source/core/rendering/RenderLayer.h b/Source/core/rendering/RenderLayer.h
index cf9654aa369d9899df8cf2db658482a291ef91a7..842e5c0699a0fe20cdbb4b2911ccb0b2cab4e4b0 100644
--- a/Source/core/rendering/RenderLayer.h
+++ b/Source/core/rendering/RenderLayer.h
@@ -478,6 +478,7 @@ public:
     bool scrollsOverflow() const;
 
     bool hasDirectReasonsForCompositing() const { return compositingReasons() & CompositingReasonComboAllDirectReasons; }
+    CompositingReasons styleDeterminedCompositingReasons() const { return compositingReasons() & CompositingReasonComboAllStyleDeterminedReasons; }
 
 private:
     bool hasOverflowControls() const;
@@ -578,6 +579,7 @@ private:
 
     bool shouldBeSelfPaintingLayer() const;
 
+
 private:
     // FIXME: We should only create the stacking node if needed.
     bool requiresStackingNode() const { return true; }
@@ -623,8 +625,8 @@ private:
     bool lostGroupedMapping() const { return m_compositingProperties.lostGroupedMapping; }
     void setLostGroupedMapping(bool b) { m_compositingProperties.lostGroupedMapping = b; }
 
-    void setCompositingReasons(CompositingReasons);
     CompositingReasons compositingReasons() const { return m_compositingProperties.compositingReasons; }
+    void setCompositingReasons(CompositingReasons, CompositingReasons mask = CompositingReasonAll);
 
     friend class CompositedLayerMapping;
     friend class RenderLayerCompositor;