Switch to null root property tree nodes [spv2]

third_party/WebKit/Source/platform/graphics/paint/ScrollPaintPropertyNode.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 ScrollPaintPropertyNode_h
 #define ScrollPaintPropertyNode_h
 
 #include "platform/PlatformExport.h"
 #include "platform/geometry/FloatSize.h"
 #include "platform/graphics/paint/TransformPaintPropertyNode.h"
 #include "wtf/PassRefPtr.h"
 #include "wtf/RefCounted.h"
 #include "wtf/RefPtr.h"
 
 #include <iosfwd>
 
 namespace blink {
 
-// A scroll node contains auxiliary scrolling information for compositor-thread
-// scrolling and includes how far an area can be scrolled, which
-// |TransformPaintPropertyNode| contains the scroll offset, etc.
+// A scroll node contains auxiliary scrolling information such as how far an
+// area can be scrolled, which |TransformPaintPropertyNode| contains the scroll
+// offset, etc.
 class PLATFORM_EXPORT ScrollPaintPropertyNode : public RefCounted<ScrollPaintPropertyNode> {
 public:
     static PassRefPtr<ScrollPaintPropertyNode> create(
         PassRefPtr<const ScrollPaintPropertyNode> parent,
         PassRefPtr<const TransformPaintPropertyNode> scrollOffsetTranslation,
         const IntSize& clip,
         const IntSize& bounds,
         bool userScrollableHorizontal,
         bool userScrollableVertical)
     {
@@ skipping 56 matching lines @@
     // TODO(pdr): Add a bit for whether this is affected by page scale.
 };
 
 // Redeclared here to avoid ODR issues.
 // See platform/testing/PaintPrinters.h.
 void PrintTo(const ScrollPaintPropertyNode&, std::ostream*);
 
 } // namespace blink
 
 #endif // ScrollPaintPropertyNode_h