Mac: Don't repaint scrollbars every frame

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 122 matching lines @@
     IntPoint convertFromContainingView(const IntPoint&) const override;
 
     void moveThumb(int pos, bool draggingDocument = false);
 
     bool isAlphaLocked() const override { return m_isAlphaLocked; }
     void setIsAlphaLocked(bool flag) override { m_isAlphaLocked = flag; }
 
     float elasticOverscroll() const override { return m_elasticOverscroll; }
     void setElasticOverscroll(float elasticOverscroll) override { m_elasticOverscroll = elasticOverscroll; }
 
+    bool trackNeedsRepaint() const override { return m_trackNeedsRepaint; }
+    void setTrackNeedsRepaint(bool trackNeedsRepaint) override { m_trackNeedsRepaint = trackNeedsRepaint; }
+    bool thumbNeedsRepaint() const override { return m_thumbNeedsRepaint; }
+    void setThumbNeedsRepaint(bool thumbNeedsRepaint) override { m_thumbNeedsRepaint = thumbNeedsRepaint; }
+
     bool overlapsResizer() const { return m_overlapsResizer; }
     void setOverlapsResizer(bool overlapsResizer) { m_overlapsResizer = overlapsResizer; }
 
     DisplayItemClient displayItemClient() const override { return toDisplayItemClient(this); }
     String debugName() const override { return m_orientation == HorizontalScrollbar ? "HorizontalScrollbar" : "VerticalScrollbar"; }
 
     void setNeedsPaintInvalidation();
 
     // Promptly unregister from the theme manager + run finalizers of derived Scrollbars.
     EAGERLY_FINALIZE();
@@ skipping 42 matching lines @@
 
     float m_elasticOverscroll;
 
 private:
     bool isScrollbar() const override { return true; }
 
     void invalidate() override { setNeedsPaintInvalidation(); }
     void invalidateRect(const IntRect&) override { setNeedsPaintInvalidation(); }
 
     float scrollableAreaCurrentPos() const;
+
+    bool m_trackNeedsRepaint;
+    bool m_thumbNeedsRepaint;
 };
 
 DEFINE_TYPE_CASTS(Scrollbar, Widget, widget, widget->isScrollbar(), widget.isScrollbar());
 
 } // namespace blink
 
 #endif // Scrollbar_h