Dispel the myth that enclosingLayer can return zero

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 1049 matching lines @@
 
         } else {
             didFullRepaint = renderer->repaintAfterLayoutIfNeeded(renderer->containerForRepaint(),
                 renderer->shouldDoFullRepaintAfterLayout(), oldRepaintRect, &newRepaintRect);
         }
 
         if (!didFullRepaint)
             renderer->repaintOverflowIfNeeded();
 
         // Repaint any scrollbars if there is a scrollable area for this renderer.
-        if (renderer->enclosingLayer()) {
-            if (RenderLayerScrollableArea* area = renderer->enclosingLayer()->scrollableArea()) {
-                if (area->hasVerticalBarDamage())
-                    renderer->repaintRectangle(area->verticalBarDamage());
-                if (area->hasHorizontalBarDamage())
-                    renderer->repaintRectangle(area->horizontalBarDamage());
-                area->resetScrollbarDamage();
-            }
+        if (RenderLayerScrollableArea* area = renderer->enclosingLayer()->scrollableArea()) {
+            if (area->hasVerticalBarDamage())
+                renderer->repaintRectangle(area->verticalBarDamage());
+            if (area->hasHorizontalBarDamage())
+                renderer->repaintRectangle(area->horizontalBarDamage());
+            area->resetScrollbarDamage();
         }
+
         // The list box has a verticalScrollbar we may need to repaint.
         if (renderer->isListBox()) {
             RenderListBox* listBox = static_cast<RenderListBox*>(renderer);
             listBox->repaintScrollbarIfNeeded();
         }
 
         renderer->clearRepaintState();
     }
 
     // Repaint the frameviews scrollbars if needed
@@ skipping 2158 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