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

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

 // Copyright 2014 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/PaintLayerPainter.h"
 
 #include "core/frame/Settings.h"
 #include "core/layout/ClipPathOperation.h"
 #include "core/layout/LayoutBlock.h"
@@ skipping 549 matching lines @@
         Optional<ScopeRecorder> scopeRecorder;
         if (needsScope)
             scopeRecorder.emplace(*context);
 
         Optional<LayerClipRecorder> clipRecorder;
 
         if (needsToClip(localPaintingInfo, fragment.backgroundRect))
             clipRecorder.emplace(*context, *m_paintLayer.layoutObject(), DisplayItem::ClipLayerOverflowControls, fragment.backgroundRect, &localPaintingInfo, fragment.paginationOffset, paintFlags);
         if (PaintLayerScrollableArea* scrollableArea = m_paintLayer.scrollableArea()) {
             CullRect cullRect(pixelSnappedIntRect(fragment.backgroundRect.rect()));
-            ScrollableAreaPainter(*scrollableArea).paintOverflowControls(context, roundedIntPoint(toPoint(fragment.layerBounds.location() - m_paintLayer.layoutBoxLocation())), cullRect, true);
+            ScrollableAreaPainter(*scrollableArea).paintOverflowControls(*context, roundedIntPoint(toPoint(fragment.layerBounds.location() - m_paintLayer.layoutBoxLocation())), cullRect, true);
         }
     }
 }
 
 void PaintLayerPainter::paintFragmentWithPhase(PaintPhase phase, const PaintLayerFragment& fragment, GraphicsContext* context, const ClipRect& clipRect, const PaintLayerPaintingInfo& paintingInfo, LayoutObject* paintingRootForLayoutObject, PaintLayerFlags paintFlags, ClipState clipState)
 {
     ASSERT(m_paintLayer.isSelfPaintingLayer());
 
     Optional<LayerClipRecorder> clipRecorder;
     if (clipState != HasClipped && paintingInfo.clipToDirtyRect && needsToClip(paintingInfo, clipRect)) {
@@ skipping 127 matching lines @@
     if (!m_paintLayer.containsDirtyOverlayScrollbars())
         return;
 
     PaintLayerPaintingInfo paintingInfo(&m_paintLayer, LayoutRect(enclosingIntRect(damageRect)), paintFlags, LayoutSize(), paintingRoot);
     paintLayer(context, paintingInfo, PaintLayerPaintingOverlayScrollbars);
 
     m_paintLayer.setContainsDirtyOverlayScrollbars(false);
 }
 
 } // namespace blink