Reduce invalidation on children-needs-layout containers

Source/core/rendering/RenderObject.h

 /*
  * Copyright (C) 2000 Lars Knoll (knoll@kde.org)
  *           (C) 2000 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  *           (C) 2004 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2009 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 509 matching lines @@
         HasBoxDecorationsAndBackgroundIsKnownToBeObscured,
         HasBoxDecorationsAndBackgroundMayBeVisible,
     };
     bool hasBoxDecorations() const { return m_bitfields.boxDecorationState() != NoBoxDecorations; }
     bool backgroundIsKnownToBeObscured();
     bool borderImageIsLoadedAndCanBeRendered() const;
     bool mustRepaintBackgroundOrBorder() const;
     bool hasBackground() const { return style()->hasBackground(); }
     bool hasEntirelyFixedBackground() const;
 
+    bool needsLayoutBecauseOfChildren() const { return needsLayout() && !selfNeedsLayout() && !needsPositionedMovementLayout() && !needsSimplifiedNormalFlowLayout(); }

[eseidel, 2014/03/21 00:37:09]

Why the needsLayout() check?  Doesn't that just check all these bools?  Don't
you want to just check the last 3?

[Julien - ping for review, 2014/03/24 18:00:01]

The logic is fine AFAICT. This is similar to needsPositionedMovementLayoutOnly()
: you check that a renderer needs layout but not for the it-needs-layout-itself
cases. I could make this more explicit by replacing needsLayout() with:
normalChildNeedsLayout() || posChildNeedsLayout().

+
     bool needsLayout() const
     {
         return m_bitfields.selfNeedsLayout() || m_bitfields.normalChildNeedsLayout() || m_bitfields.posChildNeedsLayout()
             || m_bitfields.needsSimplifiedNormalFlowLayout() || m_bitfields.needsPositionedMovementLayout();
     }
 
     bool selfNeedsLayout() const { return m_bitfields.selfNeedsLayout(); }
     bool needsPositionedMovementLayout() const { return m_bitfields.needsPositionedMovementLayout(); }
     bool needsPositionedMovementLayoutOnly() const
     {
@@ skipping 886 matching lines @@
 void showTree(const WebCore::RenderObject*);
 void showLineTree(const WebCore::RenderObject*);
 void showRenderTree(const WebCore::RenderObject* object1);
 // We don't make object2 an optional parameter so that showRenderTree
 // can be called from gdb easily.
 void showRenderTree(const WebCore::RenderObject* object1, const WebCore::RenderObject* object2);
 
 #endif
 
 #endif // RenderObject_h