Ensure PaintArtifactCompositor assigns a scroll tree index to all cc layers

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

 // Copyright 2015 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 TransformPaintPropertyNode_h
 #define TransformPaintPropertyNode_h
 
 #include "platform/PlatformExport.h"
 #include "platform/geometry/FloatPoint3D.h"
 #include "platform/graphics/CompositingReasons.h"
@@ skipping 110 matching lines @@
   // is the root transform.
   const TransformPaintPropertyNode* parent() const { return m_parent.get(); }
   bool isRoot() const { return !m_parent; }
 
   // True if this transform is for the scroll offset translation.
   bool isScrollTranslation() const { return !!m_scroll; }
   // The associated scroll node if this transform is the scroll offset for
   // scrolling, or nullptr otherwise.
   const ScrollPaintPropertyNode* scrollNode() const { return m_scroll.get(); }
 
+  // Returns the scroll node this transform scrolls with respect to. If this
+  // is a scroll translation, scrollNode() can be returned. Otherwise, a full
+  // ancestor traversal can be required.
+  const ScrollPaintPropertyNode* findEnclosingScrollNode() const;
+
   // If true, content with this transform node (or its descendant) appears in
   // the plane of its parent. This is implemented by flattening the total
   // accumulated transform from its ancestors.
   bool flattensInheritedTransform() const {
     return m_flattensInheritedTransform;
   }
 
   bool hasDirectCompositingReasons() const {
     return m_directCompositingReasons != CompositingReasonNone;
   }
@@ skipping 69 matching lines @@
   RefPtr<ScrollPaintPropertyNode> m_scroll;
 };
 
 // Redeclared here to avoid ODR issues.
 // See platform/testing/PaintPrinters.h.
 void PrintTo(const TransformPaintPropertyNode&, std::ostream*);
 
 }  // namespace blink
 
 #endif  // TransformPaintPropertyNode_h