Implement incremental paint property tree rebuilding

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

Index: third_party/WebKit/Source/platform/graphics/paint/EffectPaintPropertyNode.h
diff --git a/third_party/WebKit/Source/platform/graphics/paint/EffectPaintPropertyNode.h b/third_party/WebKit/Source/platform/graphics/paint/EffectPaintPropertyNode.h
index 94b9519480df322e950ba412367622d75bc60bf2..77eb064b2f512bb9415b29a636d9a7ea0a6b7017 100644
--- a/third_party/WebKit/Source/platform/graphics/paint/EffectPaintPropertyNode.h
+++ b/third_party/WebKit/Source/platform/graphics/paint/EffectPaintPropertyNode.h
@@ -37,6 +37,14 @@ class PLATFORM_EXPORT EffectPaintPropertyNode
     m_opacity = opacity;
   }
 
+  PassRefPtr<EffectPaintPropertyNode> clone() const {
+    return adoptRef(new EffectPaintPropertyNode(m_parent, m_opacity));
+  }
+
+  bool operator==(const EffectPaintPropertyNode& o) const {
+    return m_parent == o.m_parent && m_opacity == o.m_opacity;
+  }
+
   float opacity() const { return m_opacity; }
 
   // Parent effect or nullptr if this is the root effect.