Reduce invalidation on children-needs-layout containers

Source/core/rendering/RenderObject.h

Index: Source/core/rendering/RenderObject.h
diff --git a/Source/core/rendering/RenderObject.h b/Source/core/rendering/RenderObject.h
index 7ffb86cf19aca82d227df40ec668be67628ae97a..b823658e4b374e07241804260ea978e6831c4e46 100644
--- a/Source/core/rendering/RenderObject.h
+++ b/Source/core/rendering/RenderObject.h
@@ -527,6 +527,8 @@ public:
     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()