Paint local background colors onto foreground layer.

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 1771 matching lines @@
     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;
 
-    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.
+    // 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 (style()->canContainFixedPositionObjects() && !isFixedPos)

[chrishtr, 2016/07/29 21:04:34]

Spurious changes here?

[flackr, 2016/08/02 16:58:14]

schenney suggested I move the comment in ... while I was touching LayoutBox.cpp
to be consistent with the comment in mapLocalToAncestor. Although I guess
currently I'm not otherwise touching LayoutBox.cpp, removed.

         mode &= ~IsFixed;
-    } else if (isFixedPos) {
+    else if (isFixedPos)
         mode |= IsFixed;
-    }
 
     LayoutBoxModelObject::mapAncestorToLocal(ancestor, transformState, mode);
 }
 
 LayoutSize LayoutBox::offsetFromContainer(const LayoutObject* o) const
 {
     ASSERT(o == container());
 
     LayoutSize offset;
     if (isInFlowPositioned())
@@ skipping 3176 matching lines @@
         m_rareData->m_snapAreas->remove(&snapArea);
     }
 }
 
 SnapAreaSet* LayoutBox::snapAreas() const
 {
     return m_rareData ? m_rareData->m_snapAreas.get() : nullptr;
 }
 
 } // namespace blink