[SPv2] Flatten property trees in PaintRecordBuilder into a single display list.

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 4bc47b12d3e873d48b453d12c87ddb4e2b4e6a3a..4ee2b60335abcd8e5081ee95a2bdf8d9c6488bb6 100644
--- a/third_party/WebKit/Source/platform/graphics/paint/PropertyTreeState.h
+++ b/third_party/WebKit/Source/platform/graphics/paint/PropertyTreeState.h
@@ -29,6 +29,8 @@ class PLATFORM_EXPORT PropertyTreeState {
     DCHECK(!m_effect || !m_effect->hasOneRef());
   }
 
+  PropertyTreeState(const PropertyTreeState& other) = default;
+
   bool hasDirectCompositingReasons() const;
 
   const TransformPaintPropertyNode* transform() const {
@@ -55,6 +57,8 @@ class PLATFORM_EXPORT PropertyTreeState {
     m_effect = std::move(node);
   }
 
+  static const PropertyTreeState& root();
+
   // Returns the compositor element id, if any, for this property state. If
   // neither the effect nor transform nodes have a compositor element id then a
   // default instance is returned.