Remove negative z-index.

sky/engine/core/rendering/RenderLayerStackingNodeIterator.h

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 18 matching lines @@
  */
 
 #ifndef SKY_ENGINE_CORE_RENDERING_RENDERLAYERSTACKINGNODEITERATOR_H_
 #define SKY_ENGINE_CORE_RENDERING_RENDERLAYERSTACKINGNODEITERATOR_H_
 
 #include "sky/engine/wtf/Noncopyable.h"
 
 namespace blink {
 
 enum ChildrenIteration {
-    NegativeZOrderChildren = 1,
-    NormalFlowChildren = 1 << 1,
-    PositiveZOrderChildren = 1 << 2,
-    AllChildren = NegativeZOrderChildren | NormalFlowChildren | PositiveZOrderChildren
+    NormalFlowChildren = 1,
+    PositiveZOrderChildren = 1 << 1,
+    AllChildren = NormalFlowChildren | PositiveZOrderChildren
 };
 
 class RenderLayerStackingNode;
 
 // This iterator walks the RenderLayerStackingNode lists in the following order:
-// NegativeZOrderChildren -> NormalFlowChildren -> PositiveZOrderChildren.
+// NormalFlowChildren -> PositiveZOrderChildren.
 class RenderLayerStackingNodeIterator {
     WTF_MAKE_NONCOPYABLE(RenderLayerStackingNodeIterator);
 public:
     RenderLayerStackingNodeIterator(const RenderLayerStackingNode& root, unsigned whichChildren)
         : m_root(root)
         , m_remainingChildren(whichChildren)
         , m_index(0)
     {
     }
 
@@ skipping 23 matching lines @@
     void setIndexToLastItem();
 
     const RenderLayerStackingNode& m_root;
     unsigned m_remainingChildren;
     int m_index;
 };
 
 } // namespace blink
 
 #endif  // SKY_ENGINE_CORE_RENDERING_RENDERLAYERSTACKINGNODEITERATOR_H_