Move ScrollbarManager from core to platform and use as Scrollbar parent

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 "core/layout/ScrollAnchor.h"
 #include "platform/geometry/DoubleRect.h"
 #include "platform/geometry/FloatRect.h"
 #include "platform/geometry/LayoutRect.h"
+#include "platform/scroll/ScrollAnimatorBase.h"
 
 namespace blink {
 
 RootFrameViewport::RootFrameViewport(ScrollableArea& visual_viewport,
                                      ScrollableArea& layout_viewport)
     : visual_viewport_(visual_viewport) {
   SetLayoutViewport(layout_viewport);
 }
 
 void RootFrameViewport::SetLayoutViewport(ScrollableArea& new_layout_viewport) {
@@ skipping 432 matching lines @@
   VisualViewport().ClearScrollableArea();
 }
 
 DEFINE_TRACE(RootFrameViewport) {
   visitor->Trace(visual_viewport_);
   visitor->Trace(layout_viewport_);
   ScrollableArea::Trace(visitor);
 }
 
 }  // namespace blink