Oilpan: cleanup based on review comments after removal of TreeShared.

Source/core/rendering/RenderListBox.cpp

 /*
  * Copyright (C) 2006, 2007, 2008, 2011 Apple Inc. All rights reserved.
  *               2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 939 matching lines @@
 
     if (!m_vBar->isCustomScrollbar())
         ScrollableArea::willRemoveScrollbar(m_vBar.get(), VerticalScrollbar);
     m_vBar->removeFromParent();
     m_vBar->disconnectFromScrollableArea();
     m_vBar = nullptr;
 }
 
 void RenderListBox::setHasVerticalScrollbar(bool hasScrollbar)
 {
-    if (hasScrollbar == (m_vBar != 0))
+    if (hasScrollbar == !!m_vBar)
         return;
 
     if (hasScrollbar)
         m_vBar = createScrollbar();
     else
         destroyScrollbar();
 
     if (m_vBar)
         m_vBar->styleChanged();
 
@@ skipping 51 matching lines @@
 {
     return itemBoundingBoxRectInternal(point, listIndexToRenderListBoxIndex(index));
 }
 
 bool RenderListBox::scrollToRevealElementAtListIndex(int index)
 {
     return scrollToRevealElementAtListIndexInternal(listIndexToRenderListBoxIndex(index));
 }
 
 } // namespace WebCore