Switch RootLayerScrolls to use root transform and scroll properties

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"
@@ skipping 23 matching lines @@
         const IntSize& clip,
         const IntSize& bounds,
         bool userScrollableHorizontal,
         bool userScrollableVertical)
     {
         return adoptRef(new ScrollPaintPropertyNode(std::move(parent), std::move(scrollOffsetTranslation), clip, bounds, userScrollableHorizontal, userScrollableVertical));
     }
 
     void update(PassRefPtr<ScrollPaintPropertyNode> parent, PassRefPtr<const TransformPaintPropertyNode> scrollOffsetTranslation, const IntSize& clip, const IntSize& bounds, bool userScrollableHorizontal, bool userScrollableVertical)
     {
+        DCHECK(!isRoot());
         DCHECK(parent != this);
         m_parent = parent;
         DCHECK(scrollOffsetTranslation->matrix().isIdentityOr2DTranslation());
         m_scrollOffsetTranslation = scrollOffsetTranslation;
         m_clip = clip;
         m_bounds = bounds;
         m_userScrollableHorizontal = userScrollableHorizontal;
         m_userScrollableVertical = userScrollableVertical;
         m_mainThreadScrollingReasons = 0;
     }
@@ skipping 62 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