Avoid touching z-index in StyleAdjuster by using an isStackingContext flag instead

third_party/WebKit/Source/core/layout/LayoutObject.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  *           (C) 2004 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Google Inc. All rights reserved.
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 1924 matching lines @@
         setShouldDoFullPaintInvalidation();
 }
 
 void LayoutObject::styleWillChange(StyleDifference diff, const ComputedStyle& newStyle)
 {
     if (m_style) {
         // If our z-index changes value or our visibility changes,
         // we need to dirty our stacking context's z-order list.
         bool visibilityChanged = m_style->visibility() != newStyle.visibility()
             || m_style->zIndex() != newStyle.zIndex()
-            || m_style->hasAutoZIndex() != newStyle.hasAutoZIndex();
+            || m_style->isStackingContext() != newStyle.isStackingContext();
         if (visibilityChanged) {
             document().setAnnotatedRegionsDirty(true);
             if (AXObjectCache* cache = document().existingAXObjectCache())
                 cache->childrenChanged(parent());
         }
 
         // Keep layer hierarchy visibility bits up to date if visibility changes.
         if (m_style->visibility() != newStyle.visibility()) {
             // We might not have an enclosing layer yet because we might not be in the tree.
             if (PaintLayer* layer = enclosingLayer())
@@ skipping 1690 matching lines @@
         const blink::LayoutObject* root = object1;
         while (root->parent())
             root = root->parent();
         root->showLayoutTreeAndMark(object1, "*", object2, "-", 0);
     } else {
         WTFLogAlways("%s", "Cannot showLayoutTree. Root is (nil)");
     }
 }
 
 #endif