Implement incremental paint property tree rebuilding

third_party/WebKit/Source/platform/graphics/paint/TransformPaintPropertyNode.h

Index: third_party/WebKit/Source/platform/graphics/paint/TransformPaintPropertyNode.h
diff --git a/third_party/WebKit/Source/platform/graphics/paint/TransformPaintPropertyNode.h b/third_party/WebKit/Source/platform/graphics/paint/TransformPaintPropertyNode.h
index 945464ccd8beef9b280648aa26a2f43d57207d9b..b635aac497d34c82965b3de10e2a38a0828b5335 100644
--- a/third_party/WebKit/Source/platform/graphics/paint/TransformPaintPropertyNode.h
+++ b/third_party/WebKit/Source/platform/graphics/paint/TransformPaintPropertyNode.h
@@ -49,6 +49,19 @@ class PLATFORM_EXPORT TransformPaintPropertyNode
     m_renderingContextID = renderingContextID;
   }
 
+  PassRefPtr<TransformPaintPropertyNode> clone() const {
+    return adoptRef(new TransformPaintPropertyNode(m_matrix, m_origin, m_parent,
+                                                   m_flattensInheritedTransform,
+                                                   m_renderingContextID));
+  }
+
+  bool operator==(const TransformPaintPropertyNode& o) const {
+    return m_matrix == o.m_matrix && m_origin == o.m_origin &&
+           m_parent == o.m_parent &&
+           m_flattensInheritedTransform == o.m_flattensInheritedTransform &&
+           m_renderingContextID == o.m_renderingContextID;
+  }
+
   const TransformationMatrix& matrix() const { return m_matrix; }
   const FloatPoint3D& origin() const { return m_origin; }