Implement the algorithm to test merging and overlap in PaintArtifactCompositor.

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

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef PropertyTreeState_h
 #define PropertyTreeState_h
 
 #include "platform/graphics/paint/ClipPaintPropertyNode.h"
 #include "platform/graphics/paint/EffectPaintPropertyNode.h"
 #include "platform/graphics/paint/ScrollPaintPropertyNode.h"
@@ skipping 50 matching lines @@
 
   const ScrollPaintPropertyNode* scroll() const {
     DCHECK(!m_scroll->hasOneRef());
     return m_scroll.get();
   }
   void setScroll(const ScrollPaintPropertyNode* node) {
     m_scroll = node;
     DCHECK(!node->hasOneRef());
   }
 
+  bool hasDirectCompositingReasons() const {
+    if (!m_transform->isRoot() &&
+        m_clip->localTransformSpace() != m_transform) {
+      return m_transform->hasDirectCompositingReasons();
+    }
+    return false;
+  }
+
  private:
   RefPtr<const TransformPaintPropertyNode> m_transform;
   RefPtr<const ClipPaintPropertyNode> m_clip;
   RefPtr<const EffectPaintPropertyNode> m_effect;
   RefPtr<const ScrollPaintPropertyNode> m_scroll;
 };
+
+class PropertyTreeStateIterator {
+ public:
+  PropertyTreeStateIterator(const PropertyTreeState& properties)
+      : m_properties(properties) {}
+
+  const PropertyTreeState& current() { return m_properties; }
+  void next() {
+    if (!m_properties.transform()->isRoot() &&
+        m_properties.clip()->localTransformSpace() !=
+            m_properties.transform()) {
+      m_properties.setTransform(m_properties.transform()->parent());
+    }
+    if (!m_properties.effect()->isRoot() &&
+        m_properties.effect()->outputClip() == m_properties.clip()) {
+      m_properties.setEffect(m_properties.effect()->parent());
+    }
+    if (!m_properties.clip()->isRoot()) {
+      m_properties.setClip(m_properties.clip()->parent());
+    }
+  }
+
+  bool hasNext() {
+    if (!m_properties.transform()->isRoot() &&
+        m_properties.clip()->localTransformSpace() !=
+            m_properties.transform()) {
+      return true;
+    }
+    if (!m_properties.effect()->isRoot() &&
+        m_properties.effect()->outputClip() == m_properties.clip()) {
+      return true;
+    }
+    if (!m_properties.clip()->isRoot()) {
+      return true;
+    }
+    return false;
+  }
+
+ private:
+  PropertyTreeState m_properties;
+};
+
+inline bool operator==(const PropertyTreeState& a, const PropertyTreeState& b) {
+  return a.transform() == b.transform() && a.clip() == b.clip() &&
+         a.effect() == b.effect() && a.scroll() == b.scroll();
+}
+
 }  // namespace blink
 
 #endif  // PropertyTreeState_h