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

third_party/WebKit/Source/web/tests/FrameTestHelpers.h

 /*
  * Copyright (C) 2011 Google 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 69 matching lines @@
 // WebViewHelper includes this, so this is only needed if a test doesn't use WebViewHelper or the test
 // needs a bigger scope of mock scrollbar settings than the scope of WebViewHelper.
 class UseMockScrollbarSettings {
 public:
     UseMockScrollbarSettings()
         : m_originalMockScrollbarEnabled(Settings::mockScrollbarsEnabled())
         , m_originalOverlayScrollbarsEnabled(RuntimeEnabledFeatures::overlayScrollbarsEnabled())
     {
         Settings::setMockScrollbarsEnabled(true);
         RuntimeEnabledFeatures::setOverlayScrollbarsEnabled(true);
-        EXPECT_TRUE(ScrollbarTheme::theme()->usesOverlayScrollbars());
+        EXPECT_TRUE(ScrollbarTheme::theme().usesOverlayScrollbars());
     }
 
     ~UseMockScrollbarSettings()
     {
         Settings::setMockScrollbarsEnabled(m_originalMockScrollbarEnabled);
         RuntimeEnabledFeatures::setOverlayScrollbarsEnabled(m_originalOverlayScrollbarsEnabled);
     }
 
 private:
     bool m_originalMockScrollbarEnabled;
@@ skipping 72 matching lines @@
     WebLayerTreeView* layerTreeView() override { return m_layerTreeView.get(); }
 
 private:
     OwnPtr<WebLayerTreeView> m_layerTreeView;
 };
 
 } // namespace FrameTestHelpers
 } // namespace blink
 
 #endif // FrameTestHelpers_h