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 22bdd386c6b815855846a9895665926a705966d8..95126c4c60305f327959a19e59f38cdc9d9dfa43 100644
--- a/Source/core/rendering/RenderObject.h
+++ b/Source/core/rendering/RenderObject.h
@@ -252,6 +252,14 @@ public:
 
 #endif
 
+    bool skipInvalidationWhenLaidOutChildren() const;
+
+    // FIXME: This could be used when changing the size of a renderer without children to skip some invalidations.
+    bool rendererHasNoBoxEffect() const
+    {
+        return !style()->hasVisualOverflowingEffect() && !style()->hasBorder() && !style()->hasBackground();
+    }
+
     // Obtains the nearest enclosing block (including this block) that contributes a first-line style to our inline
     // children.
     virtual RenderBlock* firstLineBlock() const;
@@ -533,6 +541,8 @@ public:
     bool hasBackground() const { return style()->hasBackground(); }
     bool hasEntirelyFixedBackground() const;
 
+    bool needsLayoutBecauseOfChildren() const { return needsLayout() && !selfNeedsLayout() && !needsPositionedMovementLayout() && !needsSimplifiedNormalFlowLayout(); }
+
     bool needsLayout() const
     {
         return m_bitfields.selfNeedsLayout() || m_bitfields.normalChildNeedsLayout() || m_bitfields.posChildNeedsLayout()
@@ -1020,6 +1030,9 @@ public:
             parent()->setMayNeedPaintInvalidation(b);
     }
 
+    bool neededLayoutBecauseOfChildren() const { return m_bitfields.neededLayoutBecauseOfChildren(); }
+    void setNeededLayoutBecauseOfChildren(bool b) { m_bitfields.setNeededLayoutBecauseOfChildren(b); }
+
     bool shouldCheckForPaintInvalidationAfterLayout()
     {
         return layoutDidGetCalled() || mayNeedPaintInvalidation();
@@ -1147,6 +1160,7 @@ private:
             // use the other layout flags to detect the same cases. crbug.com/370118
             , m_mayNeedPaintInvalidation(false)
             , m_onlyNeededPositionedMovementLayout(false)
+            , m_neededLayoutBecauseOfChildren(false)
             , m_needsPositionedMovementLayout(false)
             , m_normalChildNeedsLayout(false)
             , m_posChildNeedsLayout(false)
@@ -1187,6 +1201,7 @@ private:
         ADD_BOOLEAN_BITFIELD(shouldDoFullPaintInvalidationIfSelfPaintingLayer, ShouldDoFullPaintInvalidationIfSelfPaintingLayer);
         ADD_BOOLEAN_BITFIELD(mayNeedPaintInvalidation, MayNeedPaintInvalidation);
         ADD_BOOLEAN_BITFIELD(onlyNeededPositionedMovementLayout, OnlyNeededPositionedMovementLayout);
+        ADD_BOOLEAN_BITFIELD(neededLayoutBecauseOfChildren, NeededLayoutBecauseOfChildren);
         ADD_BOOLEAN_BITFIELD(needsPositionedMovementLayout, NeedsPositionedMovementLayout);
         ADD_BOOLEAN_BITFIELD(normalChildNeedsLayout, NormalChildNeedsLayout);
         ADD_BOOLEAN_BITFIELD(posChildNeedsLayout, PosChildNeedsLayout);
@@ -1344,9 +1359,11 @@ inline void RenderObject::setNeedsLayoutAndFullPaintInvalidation(MarkingBehavior
 
 inline void RenderObject::clearNeedsLayout()
 {
+    // FIXME: Branch?

[leviw_travelin_and_unemployed, 2014/06/13 00:03:42]

Can you be a *little* more descriptive here? Are you only wondering if this
branch is necessary?

[Julien - ping for review, 2014/06/30 22:36:29]

This wasn't meant for public consumption but I forgot about this FIXME :(

     if (needsPositionedMovementLayoutOnly())
         setOnlyNeededPositionedMovementLayout(true);
     setLayoutDidGetCalled(true);
+    setNeededLayoutBecauseOfChildren(needsLayoutBecauseOfChildren());
     setSelfNeedsLayout(false);
     setEverHadLayout(true);
     setPosChildNeedsLayout(false);