Make rootScroller the layout viewport.

third_party/WebKit/Source/core/frame/RootFrameViewport.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 RootFrameViewport_h
 #define RootFrameViewport_h
 
 #include "core/CoreExport.h"
 #include "platform/scroll/ScrollableArea.h"
 
@@ skipping 13 matching lines @@
 class CORE_EXPORT RootFrameViewport final : public GarbageCollectedFinalized<RootFrameViewport>, public ScrollableArea {
     USING_GARBAGE_COLLECTED_MIXIN(RootFrameViewport);
 public:
     static RootFrameViewport* create(ScrollableArea& visualViewport, ScrollableArea& layoutViewport)
     {
         return new RootFrameViewport(visualViewport, layoutViewport);
     }
 
     DECLARE_VIRTUAL_TRACE();
 
+    void setLayoutViewport(ScrollableArea&);
+
     // ScrollableArea Implementation
     void setScrollPosition(const DoublePoint&, ScrollType, ScrollBehavior = ScrollBehaviorInstant) override;
     LayoutRect scrollIntoView(
         const LayoutRect& rectInContent,
         const ScrollAlignment& alignX,
         const ScrollAlignment& alignY,
         ScrollType = ProgrammaticScroll) override;
     DoubleRect visibleContentRectDouble(IncludeScrollbarsInRect = ExcludeScrollbars) const override;
     IntRect visibleContentRect(IncludeScrollbarsInRect = ExcludeScrollbars) const override;
     bool shouldUseIntegerScrollOffset() const override;
@@ skipping 43 matching lines @@
     ScrollableArea& visualViewport() const { ASSERT(m_visualViewport); return *m_visualViewport; }
     ScrollableArea& layoutViewport() const { ASSERT(m_layoutViewport); return *m_layoutViewport; }
 
     Member<ScrollableArea> m_visualViewport;
     Member<ScrollableArea> m_layoutViewport;
 };
 
 } // namespace blink
 
 #endif // RootFrameViewport_h