Use refs for non-null GraphicsContext, Scrollbar, etc. in scrollbar related code

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

 /*
  * Copyright (C) 2008 Apple 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 35 matching lines @@
     ScrollbarTheme() { }
     virtual ~ScrollbarTheme() { }
 
     // If true, then scrollbars with this theme will be painted every time
     // Scrollbar::setNeedsPaintInvalidation is called. If false, then scrollbar
     // thumb and track part painting results will be cached and not repainted
     // unless requested by Scrollbar::setThumbNeedsRepaint or
     // Scrollbar::setTrackNeedsRepaint.
     virtual bool shouldRepaintAllPartsOnInvalidation() const { return true; }
 
-    virtual void updateEnabledState(const ScrollbarThemeClient*) { }
+    virtual void updateEnabledState(const ScrollbarThemeClient&) { }
 
-    virtual bool paint(const ScrollbarThemeClient*, GraphicsContext*, const CullRect&);
+    virtual bool paint(const ScrollbarThemeClient&, GraphicsContext&, const CullRect&);
 
-    virtual ScrollbarPart hitTest(const ScrollbarThemeClient*, const IntPoint&);
+    virtual ScrollbarPart hitTest(const ScrollbarThemeClient&, const IntPoint&);
 
     virtual int scrollbarThickness(ScrollbarControlSize = RegularScrollbar) { return 0; }
     virtual int scrollbarMargin() const { return 0; }
 
     virtual ScrollbarButtonsPlacement buttonsPlacement() const { return ScrollbarButtonsPlacementSingle; }
 
     virtual bool supportsControlTints() const { return false; }
     virtual bool usesOverlayScrollbars() const { return false; }
-    virtual void updateScrollbarOverlayStyle(const ScrollbarThemeClient*) { }
+    virtual void updateScrollbarOverlayStyle(const ScrollbarThemeClient&) { }
 
     virtual bool invalidateOnMouseEnterExit() { return false; }
     virtual bool invalidateOnWindowActiveChange() const { return false; }
 
-    virtual void paintScrollCorner(GraphicsContext*, const DisplayItemClient&, const IntRect& cornerRect);
-    virtual void paintTickmarks(GraphicsContext*, const ScrollbarThemeClient*, const IntRect&) { }
+    virtual void paintScrollCorner(GraphicsContext&, const DisplayItemClient&, const IntRect& cornerRect);
+    virtual void paintTickmarks(GraphicsContext&, const ScrollbarThemeClient&, const IntRect&) { }
 
-    virtual bool shouldCenterOnThumb(const ScrollbarThemeClient*, const PlatformMouseEvent&);
-    virtual bool shouldSnapBackToDragOrigin(const ScrollbarThemeClient*, const PlatformMouseEvent&);
-    virtual bool shouldDragDocumentInsteadOfThumb(const ScrollbarThemeClient*, const PlatformMouseEvent&) { return false; }
+    virtual bool shouldCenterOnThumb(const ScrollbarThemeClient&, const PlatformMouseEvent&);
+    virtual bool shouldSnapBackToDragOrigin(const ScrollbarThemeClient&, const PlatformMouseEvent&);
+    virtual bool shouldDragDocumentInsteadOfThumb(const ScrollbarThemeClient&, const PlatformMouseEvent&) { return false; }
 
     // The position of the thumb relative to the track.
-    virtual int thumbPosition(const ScrollbarThemeClient*);
+    virtual int thumbPosition(const ScrollbarThemeClient&);
     // The length of the thumb along the axis of the scrollbar.
-    virtual int thumbLength(const ScrollbarThemeClient*);
+    virtual int thumbLength(const ScrollbarThemeClient&);
     // The position of the track relative to the scrollbar.
-    virtual int trackPosition(const ScrollbarThemeClient*);
+    virtual int trackPosition(const ScrollbarThemeClient&);
     // The length of the track along the axis of the scrollbar.
-    virtual int trackLength(const ScrollbarThemeClient*);
+    virtual int trackLength(const ScrollbarThemeClient&);
     // The opacity to be applied to the thumb.
-    virtual float thumbOpacity(const ScrollbarThemeClient*) const { return 1.0f; }
+    virtual float thumbOpacity(const ScrollbarThemeClient&) const { return 1.0f; }
 
-    virtual bool hasButtons(const ScrollbarThemeClient*) = 0;
-    virtual bool hasThumb(const ScrollbarThemeClient*) = 0;
+    virtual bool hasButtons(const ScrollbarThemeClient&) = 0;
+    virtual bool hasThumb(const ScrollbarThemeClient&) = 0;
 
-    virtual IntRect backButtonRect(const ScrollbarThemeClient*, ScrollbarPart, bool painting = false) = 0;
-    virtual IntRect forwardButtonRect(const ScrollbarThemeClient*, ScrollbarPart, bool painting = false) = 0;
-    virtual IntRect trackRect(const ScrollbarThemeClient*, bool painting = false) = 0;
-    virtual IntRect thumbRect(const ScrollbarThemeClient*);
-    virtual int thumbThickness(const ScrollbarThemeClient*);
+    virtual IntRect backButtonRect(const ScrollbarThemeClient&, ScrollbarPart, bool painting = false) = 0;
+    virtual IntRect forwardButtonRect(const ScrollbarThemeClient&, ScrollbarPart, bool painting = false) = 0;
+    virtual IntRect trackRect(const ScrollbarThemeClient&, bool painting = false) = 0;
+    virtual IntRect thumbRect(const ScrollbarThemeClient&);
+    virtual int thumbThickness(const ScrollbarThemeClient&);
 
-    virtual int minimumThumbLength(const ScrollbarThemeClient*);
+    virtual int minimumThumbLength(const ScrollbarThemeClient&);
 
-    virtual void splitTrack(const ScrollbarThemeClient*, const IntRect& track, IntRect& startTrack, IntRect& thumb, IntRect& endTrack);
+    virtual void splitTrack(const ScrollbarThemeClient&, const IntRect& track, IntRect& startTrack, IntRect& thumb, IntRect& endTrack);
 
-    virtual void paintScrollbarBackground(GraphicsContext*, const ScrollbarThemeClient*) { }
-    virtual void paintTrackBackground(GraphicsContext*, const ScrollbarThemeClient*, const IntRect&) { }
-    virtual void paintTrackPiece(GraphicsContext*, const ScrollbarThemeClient*, const IntRect&, ScrollbarPart) { }
-    virtual void paintButton(GraphicsContext*, const ScrollbarThemeClient*, const IntRect&, ScrollbarPart) { }
-    virtual void paintThumb(GraphicsContext*, const ScrollbarThemeClient*, const IntRect&) { }
+    virtual void paintScrollbarBackground(GraphicsContext&, const ScrollbarThemeClient&) { }
+    virtual void paintTrackBackground(GraphicsContext&, const ScrollbarThemeClient&, const IntRect&) { }
+    virtual void paintTrackPiece(GraphicsContext&, const ScrollbarThemeClient&, const IntRect&, ScrollbarPart) { }
+    virtual void paintButton(GraphicsContext&, const ScrollbarThemeClient&, const IntRect&, ScrollbarPart) { }
+    virtual void paintThumb(GraphicsContext&, const ScrollbarThemeClient&, const IntRect&) { }
 
     virtual int maxOverlapBetweenPages() { return std::numeric_limits<int>::max(); }
 
     virtual double initialAutoscrollTimerDelay() { return 0.25; }
     virtual double autoscrollTimerDelay() { return 0.05; }
 
-    virtual IntRect constrainTrackRectToTrackPieces(const ScrollbarThemeClient*, const IntRect& rect) { return rect; }
+    virtual IntRect constrainTrackRectToTrackPieces(const ScrollbarThemeClient&, const IntRect& rect) { return rect; }
 
-    virtual void registerScrollbar(ScrollbarThemeClient*) { }
-    virtual void unregisterScrollbar(ScrollbarThemeClient*) { }
+    virtual void registerScrollbar(ScrollbarThemeClient&) { }
+    virtual void unregisterScrollbar(ScrollbarThemeClient&) { }
 
     virtual bool isMockTheme() const { return false; }
 
-    static ScrollbarTheme* theme();
+    static ScrollbarTheme& theme();
 
     static void setMockScrollbarsEnabled(bool flag);
     static bool mockScrollbarsEnabled();
 
 protected:
     static DisplayItem::Type buttonPartToDisplayItemType(ScrollbarPart);
     static DisplayItem::Type trackPiecePartToDisplayItemType(ScrollbarPart);
 
 private:
-    static ScrollbarTheme* nativeTheme(); // Must be implemented to return the correct theme subclass.
+    static ScrollbarTheme& nativeTheme(); // Must be implemented to return the correct theme subclass.
     static bool gMockScrollbarsEnabled;
 };
 
 }
 #endif