Eagerly invalidate when a layer becomes stacking context

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 244 matching lines @@
     }
   }
 
   LayoutObject::willBeDestroyed();
 
   destroyLayer();
 }
 
 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.isStackingContext()) {
+  // This object's layer may begin or cease to be a stacking context, in which
+  // case the paint invalidation container of this object and descendants may
+  // change. Thus we need to invalidate paint eagerly for all such children.
+  // PaintLayerCompositor::paintInvalidationOnCompositingChange() doesn't work
+  // for the case because we can only see the new paintInvalidationContainer
+  // during compositing update.
+  if (style() &&
+      (style()->isStackingContext() != newStyle.isStackingContext())) {
     // The following disablers are valid because we need to invalidate based on
     // the current status.
     DisableCompositingQueryAsserts compositingDisabler;
     DisablePaintInvalidationStateAsserts paintDisabler;
     ObjectPaintInvalidator(*this)
         .invalidatePaintIncludingNonCompositingDescendants();
   }
 
   FloatStateForStyleChange::setWasFloating(this, isFloating());
 
@@ skipping 1184 matching lines @@
   if (rootElementStyle->hasBackground())
     return false;
 
   if (node() != document().firstBodyElement())
     return false;
 
   return true;
 }
 
 }  // namespace blink