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

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

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  *           (C) 2005, 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Google 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
@@ skipping 133 matching lines @@
 }
 
 void LayoutBoxModelObject::styleWillChange(StyleDifference diff, const ComputedStyle& newStyle)
 {
     // This object's layer may cease to be a stacking context, in which case the paint
     // invalidation container of the children may change. Thus we need to invalidate paint
     // eagerly for all such children.
     if (hasLayer()
         && enclosingLayer()->stackingNode()
         && enclosingLayer()->stackingNode()->isStackingContext()
-        && newStyle.hasAutoZIndex()) {
+        && !newStyle.isStackingContext()) {
         // The following disablers are valid because we need to invalidate based on the current
         // status.
         DisableCompositingQueryAsserts compositingDisabler;
         DisablePaintInvalidationStateAsserts paintDisabler;
         invalidatePaintIncludingNonCompositingDescendants();
     }
 
     FloatStateForStyleChange::setWasFloating(this, isFloating());
 
     if (const ComputedStyle* oldStyle = style()) {
@@ skipping 948 matching lines @@
     if (rootElementStyle->hasBackground())
         return false;
 
     if (node() != document().firstBodyElement())
         return false;
 
     return true;
 }
 
 } // namespace blink