Make rootScroller the layout viewport.

third_party/WebKit/Source/core/frame/RootFrameViewport.cpp

 // 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.
 
 #include "core/frame/RootFrameViewport.h"
 
 #include "core/frame/FrameView.h"
 #include "core/layout/ScrollAlignment.h"
 #include "platform/geometry/DoubleRect.h"
 #include "platform/geometry/FloatRect.h"
 #include "platform/geometry/LayoutRect.h"
 
 namespace blink {
 
 RootFrameViewport::RootFrameViewport(ScrollableArea& visualViewport, ScrollableArea& layoutViewport)
     : m_visualViewport(visualViewport)
     , m_layoutViewport(layoutViewport)
 {
 }
 
+void RootFrameViewport::setLayoutViewport(ScrollableArea& newLayoutViewport)
+{
+    m_layoutViewport = &newLayoutViewport;
+}
+
 void RootFrameViewport::updateScrollAnimator()
 {
     scrollAnimator().setCurrentPosition(toFloatPoint(scrollOffsetFromScrollAnimators()));
 }
 
 DoublePoint RootFrameViewport::scrollOffsetFromScrollAnimators() const
 {
     return visualViewport().scrollAnimator().currentPosition() + layoutViewport().scrollAnimator().currentPosition();
 }
 
@@ skipping 311 matching lines @@
 }
 
 DEFINE_TRACE(RootFrameViewport)
 {
     visitor->trace(m_visualViewport);
     visitor->trace(m_layoutViewport);
     ScrollableArea::trace(visitor);
 }
 
 } // namespace blink