Implement the algorithm to test merging and overlap in PaintArtifactCompositor.

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

Index: third_party/WebKit/Source/platform/graphics/paint/PropertyTreeState.h
diff --git a/third_party/WebKit/Source/platform/graphics/paint/PropertyTreeState.h b/third_party/WebKit/Source/platform/graphics/paint/PropertyTreeState.h
index 6a6f1e2eabc3cdfe92fe78ec554645933f14b608..a3116582bad6fd18d567ef3d521ef4c3c37b83b1 100644
--- a/third_party/WebKit/Source/platform/graphics/paint/PropertyTreeState.h
+++ b/third_party/WebKit/Source/platform/graphics/paint/PropertyTreeState.h
@@ -68,12 +68,67 @@ class PropertyTreeState {
     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