Remove negative z-index.

sky/engine/core/rendering/style/RenderStyle.h

 /*
  * Copyright (C) 2000 Lars Knoll (knoll@kde.org)
  *           (C) 2000 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2003, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
@@ skipping 988 matching lines @@
 
     void setCursor(ECursor c) { inherited_flags._cursor_style = c; }
     void addCursor(PassRefPtr<StyleImage>, const IntPoint& hotSpot = IntPoint());
     void setCursorList(PassRefPtr<CursorList>);
     void clearCursorList();
 
     void setIsLink(bool b) { noninherited_flags.isLink = b; }
 
     bool hasAutoZIndex() const { return m_box->hasAutoZIndex(); }
     void setHasAutoZIndex() { SET_VAR(m_box, m_hasAutoZIndex, true); SET_VAR(m_box, m_zIndex, 0); }
-    int zIndex() const { return m_box->zIndex(); }
-    void setZIndex(int v) { SET_VAR(m_box, m_hasAutoZIndex, false); SET_VAR(m_box, m_zIndex, v); }
+    unsigned zIndex() const { return m_box->zIndex(); }
+    void setZIndex(unsigned v) { SET_VAR(m_box, m_hasAutoZIndex, false); SET_VAR(m_box, m_zIndex, v); }
 
     void setHasAutoWidows() { SET_VAR(rareInheritedData, m_hasAutoWidows, true); SET_VAR(rareInheritedData, widows, initialWidows()); }
     void setWidows(short w) { SET_VAR(rareInheritedData, m_hasAutoWidows, false); SET_VAR(rareInheritedData, widows, w); }
 
     void setHasAutoOrphans() { SET_VAR(rareInheritedData, m_hasAutoOrphans, true); SET_VAR(rareInheritedData, orphans, initialOrphans()); }
     void setOrphans(short o) { SET_VAR(rareInheritedData, m_hasAutoOrphans, false); SET_VAR(rareInheritedData, orphans, o); }
 
     // For valid values of page-break-inside see http://www.w3.org/TR/CSS21/page.html#page-break-props
     void setPageBreakInside(EPageBreak b) { ASSERT(b == PBAUTO || b == PBAVOID); noninherited_flags.pageBreakInside = b; }
     void setPageBreakBefore(EPageBreak b) { noninherited_flags.pageBreakBefore = b; }
@@ skipping 357 matching lines @@
 
     rareInheritedData.access()->m_textOrientation = textOrientation;
     return true;
 }
 
 float calcBorderRadiiConstraintScaleFor(const FloatRect&, const FloatRoundedRect::Radii&);
 
 } // namespace blink
 
 #endif  // SKY_ENGINE_CORE_RENDERING_STYLE_RENDERSTYLE_H_