Ensure that we consistently check contains: paint for fixed position containment.

third_party/WebKit/Source/core/layout/LayoutBox.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, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2013 Adobe Systems Incorporated. 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 1704 matching lines @@
         return std::min(fillAvailableExtent, fillFallbackExtent);
     }
 
     // Use the content box logical height as specified by the style.
     return cb->adjustContentBoxLogicalHeightForBoxSizing(LayoutUnit(logicalHeightLength.value()));
 }
 
 void LayoutBox::mapLocalToAncestor(const LayoutBoxModelObject* ancestor, TransformState& transformState, MapCoordinatesFlags mode) const
 {
     bool isFixedPos = style()->position() == FixedPosition;
-    bool hasTransform = hasLayer() && layer()->transform();
-    // If this box has a transform, it acts as a fixed position container for fixed descendants,
+
+    // If this box has a transform or contains paint, it acts as a fixed position container for fixed descendants,
     // and may itself also be fixed position. So propagate 'fixed' up only if this box is fixed position.
-    if (hasTransform && !isFixedPos)
+    if (style()->canContainFixedPositionObjects() && !isFixedPos)
         mode &= ~IsFixed;
     else if (isFixedPos)
         mode |= IsFixed;
 
     LayoutBoxModelObject::mapLocalToAncestor(ancestor, transformState, mode);
 }
 
 void LayoutBox::mapAncestorToLocal(const LayoutBoxModelObject* ancestor, TransformState& transformState, MapCoordinatesFlags mode) const
 {
     if (this == ancestor)
         return;
 
     bool isFixedPos = style()->position() == FixedPosition;
-    bool hasTransform = hasLayer() && layer()->transform();
-    if (hasTransform && !isFixedPos) {
-        // If this box has a transform, it acts as a fixed position container for fixed descendants,
+
+    if (style()->canContainFixedPositionObjects() && !isFixedPos) {
+        // If this box has a transform or contains paint, it acts as a fixed position container for fixed descendants,
         // and may itself also be fixed position. So propagate 'fixed' up only if this box is fixed position.
         mode &= ~IsFixed;
     } else if (isFixedPos) {
         mode |= IsFixed;
     }
 
     LayoutBoxModelObject::mapAncestorToLocal(ancestor, transformState, mode);
 }
 
 LayoutSize LayoutBox::offsetFromContainer(const LayoutObject* o) const
@@ skipping 3171 matching lines @@
         m_rareData->m_snapAreas->remove(&snapArea);
     }
 }
 
 SnapAreaSet* LayoutBox::snapAreas() const
 {
     return m_rareData ? m_rareData->m_snapAreas.get() : nullptr;
 }
 
 } // namespace blink