Remove negative z-index.

sky/engine/core/rendering/style/StyleBoxData.cpp

 /*
  * Copyright (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *
  * 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
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 10 matching lines @@
 
 #include "sky/engine/config.h"
 #include "sky/engine/core/rendering/style/StyleBoxData.h"
 
 #include "sky/engine/core/rendering/style/RenderStyle.h"
 
 namespace blink {
 
 struct SameSizeAsStyleBoxData : public RefCounted<SameSizeAsStyleBoxData> {
     Length length[7];
-    int m_zIndex;
+    unsigned m_zIndex;
     uint32_t bitfields;
 };
 
 COMPILE_ASSERT(sizeof(StyleBoxData) == sizeof(SameSizeAsStyleBoxData), StyleBoxData_should_not_grow);
 
 StyleBoxData::StyleBoxData()
     : m_minWidth(RenderStyle::initialMinSize())
     , m_maxWidth(RenderStyle::initialMaxSize())
     , m_minHeight(RenderStyle::initialMinSize())
     , m_maxHeight(RenderStyle::initialMaxSize())
@@ skipping 30 matching lines @@
            && m_maxHeight == o.m_maxHeight
            && m_verticalAlign == o.m_verticalAlign
            && m_zIndex == o.m_zIndex
            && m_hasAutoZIndex == o.m_hasAutoZIndex
            && m_boxSizing == o.m_boxSizing
            && m_boxDecorationBreak == o.m_boxDecorationBreak
             ;
 }
 
 } // namespace blink