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

third_party/WebKit/Source/platform/exported/WebScrollbarThemeGeometryNative.h

Index: third_party/WebKit/Source/platform/exported/WebScrollbarThemeGeometryNative.h
diff --git a/third_party/WebKit/Source/platform/exported/WebScrollbarThemeGeometryNative.h b/third_party/WebKit/Source/platform/exported/WebScrollbarThemeGeometryNative.h
index 0030f8c9973cf357708c0fbbb39678587a107014..29f80f93ca86163ba52f1bc7ed555e7938dfbd7f 100644
--- a/third_party/WebKit/Source/platform/exported/WebScrollbarThemeGeometryNative.h
+++ b/third_party/WebKit/Source/platform/exported/WebScrollbarThemeGeometryNative.h
@@ -38,7 +38,7 @@ class WebScrollbar;
 
 class PLATFORM_EXPORT WebScrollbarThemeGeometryNative : public WebScrollbarThemeGeometry {
 public:
-    static PassOwnPtr<WebScrollbarThemeGeometryNative> create(ScrollbarTheme*);
+    static PassOwnPtr<WebScrollbarThemeGeometryNative> create(ScrollbarTheme&);
 
     // WebScrollbarThemeGeometry overrides
     WebScrollbarThemeGeometryNative* clone() const override;
@@ -60,12 +60,12 @@ public:
     void splitTrack(WebScrollbar*, const WebRect& track, WebRect& startTrack, WebRect& thumb, WebRect& endTrack) override;
 
 private:
-    explicit WebScrollbarThemeGeometryNative(ScrollbarTheme*);
+    explicit WebScrollbarThemeGeometryNative(ScrollbarTheme&);
 
     // The theme is not owned by this class. It is assumed that the theme is a
     // static pointer and its lifetime is essentially infinite. Only thread-safe
     // functions on the theme can be called by this theme.
-    ScrollbarTheme* m_theme;
+    ScrollbarTheme& m_theme;
 };
 
 } // namespace blink