Move ScrollbarManager from core to platform and use as Scrollbar parent

third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h

Index: third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h
diff --git a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h
index a00b42bb565f10b645cde6b8b1ffc33bbdfc8a6b..be2f89c7aa92c678b908e35c9ecb9ff0592f29c2 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h
+++ b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.h
@@ -50,8 +50,8 @@
 #include "core/page/scrolling/StickyPositionScrollingConstraints.h"
 #include "core/paint/PaintInvalidationCapableScrollableArea.h"
 #include "core/paint/PaintLayerFragment.h"
-#include "core/paint/ScrollbarManager.h"
 #include "platform/heap/Handle.h"
+#include "platform/scroll/ScrollbarManager.h"
 #include "platform/wtf/PtrUtil.h"
 
 namespace blink {
@@ -139,7 +139,7 @@ class CORE_EXPORT PaintLayerScrollableArea final
     // a new one.
    public:
     ScrollbarManager(PaintLayerScrollableArea& scroller)
-        : blink::ScrollbarManager(scroller) {}
+        : blink::ScrollbarManager() {}
 
     void SetHasHorizontalScrollbar(bool has_scrollbar) override;
     void SetHasVerticalScrollbar(bool has_scrollbar) override;