Let DeprecatedPaintLayer be client of subsequence display items

Source/core/paint/DeprecatedPaintLayer.h

Index: Source/core/paint/DeprecatedPaintLayer.h
diff --git a/Source/core/paint/DeprecatedPaintLayer.h b/Source/core/paint/DeprecatedPaintLayer.h
index 07155d41d34941c5cb88ad850524513c4390f61a..839d878686414d62f287687dcf94c86771d23f8a 100644
--- a/Source/core/paint/DeprecatedPaintLayer.h
+++ b/Source/core/paint/DeprecatedPaintLayer.h
@@ -551,6 +551,9 @@ public:
     void setNeedsRepaint();
     void clearNeedsRepaint() { m_needsRepaint = false; }
 
+    // For subsequence display items.
+    DisplayItemClient displayItemClient() const { return toDisplayItemClient(this); }
+
 private:
     // Bounding box in the coordinates of this layer.
     LayoutRect logicalBoundingBox() const;