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

third_party/WebKit/Source/core/paint/PaintInvalidationCapableScrollableArea.cpp

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "config.h"
 #include "core/paint/PaintInvalidationCapableScrollableArea.h"
 
 #include "core/frame/Settings.h"
 #include "core/html/HTMLFrameOwnerElement.h"
 #include "core/layout/LayoutBox.h"
 #include "core/layout/LayoutScrollbar.h"
 #include "core/layout/LayoutScrollbarPart.h"
 #include "core/layout/PaintInvalidationState.h"
 #include "core/paint/PaintLayer.h"
 #include "platform/graphics/GraphicsLayer.h"
 
 namespace blink {
 
-void PaintInvalidationCapableScrollableArea::willRemoveScrollbar(Scrollbar* scrollbar, ScrollbarOrientation orientation)
+void PaintInvalidationCapableScrollableArea::willRemoveScrollbar(Scrollbar& scrollbar, ScrollbarOrientation orientation)
 {
-    if (!scrollbar->isCustomScrollbar()
+    if (!scrollbar.isCustomScrollbar()
         && !(orientation == HorizontalScrollbar ? layerForHorizontalScrollbar() : layerForVerticalScrollbar()))
-        boxForScrollControlPaintInvalidation().invalidateDisplayItemClient(*scrollbar);
+        boxForScrollControlPaintInvalidation().invalidateDisplayItemClient(scrollbar);
 
     ScrollableArea::willRemoveScrollbar(scrollbar, orientation);
 }
 
 static LayoutRect scrollControlPaintInvalidationRect(const IntRect& scrollControlRect, const LayoutBox& box, const PaintInvalidationState& paintInvalidationState, const LayoutBoxModelObject& paintInvalidationContainer)
 {
     LayoutRect paintInvalidationRect(scrollControlRect);
     if (!paintInvalidationRect.isEmpty())
         PaintLayer::mapRectToPaintInvalidationBacking(&box, &paintInvalidationContainer, paintInvalidationRect, &paintInvalidationState);
     return paintInvalidationRect;
@@ skipping 82 matching lines @@
 }
 
 void PaintInvalidationCapableScrollableArea::clearPreviousPaintInvalidationRects()
 {
     m_horizontalScrollbarPreviousPaintInvalidationRect = LayoutRect();
     m_verticalScrollbarPreviousPaintInvalidationRect = LayoutRect();
     m_scrollCornerPreviousPaintInvalidationRect = LayoutRect();
 }
 
 } // namespace blink