Scrollbar no longer inherits from FrameViewBase.

third_party/WebKit/Source/platform/scroll/Scrollbar.h

 /*
  * Copyright (C) 2004, 2006 Apple Computer, Inc.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 27 matching lines @@
 
 class CullRect;
 class GraphicsContext;
 class IntRect;
 class PlatformChromeClient;
 class ScrollableArea;
 class ScrollbarTheme;
 class WebGestureEvent;
 class WebMouseEvent;
 
-class PLATFORM_EXPORT Scrollbar : public FrameViewBase,
+class PLATFORM_EXPORT Scrollbar : public GarbageCollectedFinalized<Scrollbar>,
                                   public ScrollbarThemeClient,
                                   public DisplayItemClient {
  public:
   static Scrollbar* Create(ScrollableArea* scrollable_area,
                            ScrollbarOrientation orientation,
                            ScrollbarControlSize size,
                            PlatformChromeClient* chrome_client) {
     return new Scrollbar(scrollable_area, orientation, size, chrome_client);
   }
 
   // Theme object ownership remains with the caller and it must outlive the
   // scrollbar.
   static Scrollbar* CreateForTesting(ScrollableArea* scrollable_area,
                                      ScrollbarOrientation orientation,
                                      ScrollbarControlSize size,
                                      ScrollbarTheme* theme) {
     return new Scrollbar(scrollable_area, orientation, size, nullptr, theme);
   }
 
   ~Scrollbar() override;
 
   // ScrollbarThemeClient implementation.
-  int X() const override { return FrameViewBase::X(); }
-  int Y() const override { return FrameViewBase::Y(); }
-  int Width() const override { return FrameViewBase::Width(); }
-  int Height() const override { return FrameViewBase::Height(); }
-  IntSize Size() const override { return FrameViewBase::Size(); }
-  IntPoint Location() const override { return FrameViewBase::Location(); }
+  int X() const override { return frame_rect_.X(); }
+  int Y() const override { return frame_rect_.Y(); }
+  int Width() const override { return frame_rect_.Width(); }
+  int Height() const override { return frame_rect_.Height(); }
+  IntSize Size() const override { return frame_rect_.Size(); }
+  IntPoint Location() const override { return frame_rect_.Location(); }
 
-  FrameViewBase* Parent() const override { return FrameViewBase::Parent(); }
-  FrameViewBase* Root() const override { return FrameViewBase::Root(); }
+  virtual void SetParent(FrameViewBase* parent) { parent_ = parent; }

[szager1, 2017/04/21 08:37:52]

Why virtual?

[joelhockey, 2017/04/21 09:56:10]

LayoutScrollbar overrides to call a private UpdateScrollbarParts.
https://cs.chromium.org/chromium/src/third_party/WebKit/Source/core/layout/La...

+  FrameViewBase* Parent() const { return parent_; }
 
-  void SetFrameRect(const IntRect&) override;
-  IntRect FrameRect() const override { return FrameViewBase::FrameRect(); }
+  void SetFrameRect(const IntRect&);

[szager1, 2017/04/21 08:37:52]

Shouldn't this still be an override?

[joelhockey, 2017/04/21 09:56:10]

Yes, thanks.  It is still overriding ScrollbarThemeClient::SetFrameRect. 
Shouldn't I get a compile error or warning?

+  IntRect FrameRect() const override { return frame_rect_; }
 
   ScrollbarOverlayColorTheme GetScrollbarOverlayColorTheme() const override;
   void GetTickmarks(Vector<IntRect>&) const override;
   bool IsScrollableAreaActive() const override;
 
   IntPoint ConvertFromRootFrame(
       const IntPoint& point_in_root_frame) const override;
 
   bool IsCustomScrollbar() const override { return false; }
   ScrollbarOrientation Orientation() const override { return orientation_; }
@@ skipping 56 matching lines @@
   void MouseExited();
 
   // Used by some platform scrollbars to know when they've been released from
   // capture.
   void MouseUp(const WebMouseEvent&);
   void MouseDown(const WebMouseEvent&);
 
   ScrollbarTheme& GetTheme() const { return theme_; }
 
   IntRect ConvertToContainingFrameViewBase(const IntRect&) const;
-  IntPoint ConvertFromContainingFrameViewBase(const IntPoint&) const override;
+  IntPoint ConvertFromContainingFrameViewBase(const IntPoint&) const;
 
   void MoveThumb(int pos, bool dragging_document = false);
 
   float ElasticOverscroll() const override { return elastic_overscroll_; }
   void SetElasticOverscroll(float elastic_overscroll) override {
     elastic_overscroll_ = elastic_overscroll;
   }
 
   // Use setNeedsPaintInvalidation to cause the scrollbar (or parts thereof)
   // to repaint.
@@ skipping 62 matching lines @@
   bool dragging_document_;
   int document_drag_pos_;
 
   bool enabled_;
 
   TaskRunnerTimer<Scrollbar> scroll_timer_;
 
   float elastic_overscroll_;
 
  private:
-  bool IsScrollbar() const override { return true; }
-
   void Invalidate() override { SetNeedsPaintInvalidation(kAllParts); }
   void InvalidateRect(const IntRect&) override {
     SetNeedsPaintInvalidation(kAllParts);
   }
 
   float ScrollableAreaCurrentPos() const;
   float ScrollableAreaTargetPos() const;
   bool ThumbWillBeUnderMouse() const;
 
   int theme_scrollbar_thickness_;
   bool track_needs_repaint_;
   bool thumb_needs_repaint_;
   LayoutRect visual_rect_;
+  Member<FrameViewBase> parent_;

[haraken, 2017/04/21 08:42:03]

I think this can be Member<FrameView>. I think the parent of Scrollbar is
guaranteed to be FrameView.

[joelhockey, 2017/04/21 09:56:10]

I wish!  That would have made my work easier ;-)
No, FrameView is not visible to platform.

+  IntRect frame_rect_;
 };
 
-DEFINE_TYPE_CASTS(Scrollbar,
-                  FrameViewBase,
-                  frameViewBase,
-                  frameViewBase->IsScrollbar(),
-                  frameViewBase.IsScrollbar());
-
 }  // namespace blink
 
 #endif  // Scrollbar_h