Don't call RenderObject::enclosingLayer on a null pointer

Source/core/frame/FrameView.cpp

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999 Lars Knoll <knoll@kde.org>
  *                     1999 Antti Koivisto <koivisto@kde.org>
  *                     2000 Dirk Mueller <mueller@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *           (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
@@ skipping 2717 matching lines @@
     if (m_paintBehavior == PaintBehaviorNormal)
         document->markers().invalidateRenderedRectsForMarkersInRect(rect);
 
     if (document->printing())
         m_paintBehavior |= PaintBehaviorFlattenCompositingLayers;
 
     ASSERT(!m_isPainting);
     m_isPainting = true;
 
     // m_nodeToDraw is used to draw only one element (and its descendants)
-    RenderObject* eltRenderer = m_nodeToDraw ? m_nodeToDraw->renderer() : 0;
+    RenderObject* renderer = m_nodeToDraw ? m_nodeToDraw->renderer() : 0;
     RenderLayer* rootLayer = renderView->layer();
 
 #ifndef NDEBUG
     renderView->assertSubtreeIsLaidOut();
     RenderObject::SetLayoutNeededForbiddenScope forbidSetNeedsLayout(rootLayer->renderer());
 #endif
 
-    RenderObject* enclosingLayerRenderer = eltRenderer->enclosingLayer() ? eltRenderer->enclosingLayer()->renderer() : eltRenderer;
+    RenderObject* enclosingLayerRenderer = renderer ? renderer->enclosingLayer()->renderer() : 0;
     rootLayer->paint(p, rect, m_paintBehavior, enclosingLayerRenderer);
 
     if (rootLayer->containsDirtyOverlayScrollbars())
-        rootLayer->paintOverlayScrollbars(p, rect, m_paintBehavior, eltRenderer);
+        rootLayer->paintOverlayScrollbars(p, rect, m_paintBehavior, renderer);
 
     m_isPainting = false;
 
     m_paintBehavior = oldPaintBehavior;
     m_lastPaintTime = currentTime();
 
     // Regions may have changed as a result of the visibility/z-index of element changing.
     if (document->annotatedRegionsDirty())
         updateAnnotatedRegions();
 
@@ skipping 486 matching lines @@
 void FrameView::willRemoveScrollbar(Scrollbar* scrollbar, ScrollbarOrientation orientation)
 {
     ScrollableArea::willRemoveScrollbar(scrollbar, orientation);
     if (AXObjectCache* cache = axObjectCache()) {
         cache->remove(scrollbar);
         cache->handleScrollbarUpdate(this);
     }
 }
 
 } // namespace WebCore