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

third_party/WebKit/Source/core/dom/Element.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Peter Kelly (pmk@post.com)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2007 David Smith (catfish.man@gmail.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012, 2013 Apple Inc. All rights reserved.
  *           (C) 2007 Eric Seidel (eric@webkit.org)
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 1656 matching lines @@
     if (ElementAnimations* elementAnimations = this->elementAnimations()) {
         elementAnimations->cssAnimations().maybeApplyPendingUpdate(this);
         elementAnimations->updateAnimationFlags(*style);
     }
 
     if (style->hasTransform()) {
         if (const StylePropertySet* inlineStyle = this->inlineStyle())
             style->setHasInlineTransform(inlineStyle->hasProperty(CSSPropertyTransform));
     }
 
+    style->updateIsStackingContext(this == document().documentElement(), isInTopLayer());
+
     return style.release();
 }
 
 PassRefPtr<ComputedStyle> Element::originalStyleForLayoutObject()
 {
     DCHECK(document().inStyleRecalc());
     return document().ensureStyleResolver().styleForElement(this);
 }
 
 void Element::recalcStyle(StyleRecalcChange change, Text* nextTextSibling)
@@ skipping 2030 matching lines @@
 
 DEFINE_TRACE_WRAPPERS(Element)
 {
     if (hasRareData()) {
         visitor->traceWrappers(elementRareData());
     }
     ContainerNode::traceWrappers(visitor);
 }
 
 } // namespace blink