Improve positioned/percentHeight descendant/container tracking

third_party/WebKit/Source/core/layout/LayoutBlock.h

Index: third_party/WebKit/Source/core/layout/LayoutBlock.h
diff --git a/third_party/WebKit/Source/core/layout/LayoutBlock.h b/third_party/WebKit/Source/core/layout/LayoutBlock.h
index 2ae34b93f839fef30594c5d818e5b9ad6f845d69..122343d57e1e6dcd22e0cc5c25ed1ee97db3817b 100644
--- a/third_party/WebKit/Source/core/layout/LayoutBlock.h
+++ b/third_party/WebKit/Source/core/layout/LayoutBlock.h
@@ -43,12 +43,30 @@ class LayoutInline;
 class WordMeasurement;
 
 typedef WTF::ListHashSet<LayoutBox*, 16> TrackedLayoutBoxListHashSet;
-typedef WTF::HashMap<const LayoutBlock*, OwnPtr<TrackedLayoutBoxListHashSet>> TrackedDescendantsMap;
-typedef WTF::HashMap<const LayoutBox*, OwnPtr<HashSet<LayoutBlock*>>> TrackedContainerMap;
 typedef Vector<WordMeasurement, 64> WordMeasurements;
 
 enum ContainingBlockState { NewContainingBlock, SameContainingBlock };
 
+class LayoutBlockRareData : public LayoutBoxRareData {
+public:
+    // This set keeps track of the positioned objects associated with a containing
+    // block.
+    //
+    // This set is populated during layout. It is kept across layouts to handle
+    // that we skip unchanged sub-trees during layout, in such a way that we are
+    // able to lay out deeply nested out-of-flow descendants if their containing
+    // block got laid out. The set could be invalidated during style change but
+    // keeping track of containing blocks at that time is complicated (we are in
+    // the middle of recomputing the style so we can't rely on any of its
+    // information), which is why it's easier to just update it for every layout.
+    OwnPtr<TrackedLayoutBoxListHashSet> m_positionedDescendants;
+
+    // This set keeps track of the descendants whose 'height' is percentage associated
+    // with a containing block. Like |m_positionedDescendants|, it is also recomputed
+    // for every layout (see the comment above about why).
+    OwnPtr<TrackedLayoutBoxListHashSet> m_percentHeightDescendants;
+};
+
 // LayoutBlock is the class that is used by any LayoutObject
 // that is a containing block.
 // http://www.w3.org/TR/CSS2/visuren.html#containing-block
@@ -156,10 +174,10 @@ public:
     virtual void layoutBlock(bool relayoutChildren);
 
     void insertPositionedObject(LayoutBox*);
-    static void removePositionedObject(LayoutBox*);
+    void removePositionedObject(LayoutBox*);
     void removePositionedObjects(LayoutBlock*, ContainingBlockState = SameContainingBlock);
 
-    TrackedLayoutBoxListHashSet* positionedObjects() const;
+    TrackedLayoutBoxListHashSet* positionedObjects() const { return layoutBlockRareData() ? layoutBlockRareData()->m_positionedDescendants.get() : nullptr; }
     bool hasPositionedObjects() const
     {
         TrackedLayoutBoxListHashSet* objects = positionedObjects();
@@ -167,13 +185,10 @@ public:
     }
 
     void addPercentHeightDescendant(LayoutBox*);
-    static void removePercentHeightDescendant(LayoutBox*);
-    static bool hasPercentHeightContainerMap();
-    static bool hasPercentHeightDescendant(LayoutBox*);
-    static void clearPercentHeightDescendantsFrom(LayoutBox*);
-    static void removePercentHeightDescendantIfNeeded(LayoutBox*);
+    void removePercentHeightDescendant(LayoutBox*);
+    bool hasPercentHeightDescendant(LayoutBox*);
 
-    TrackedLayoutBoxListHashSet* percentHeightDescendants() const;
+    TrackedLayoutBoxListHashSet* percentHeightDescendants() const { return layoutBlockRareData() ? layoutBlockRareData()->m_percentHeightDescendants.get() : nullptr; }
     bool hasPercentHeightDescendants() const
     {
         TrackedLayoutBoxListHashSet* descendants = percentHeightDescendants();
@@ -399,9 +414,6 @@ private:
 
     bool isSelfCollapsingBlock() const override;
 
-    void insertIntoTrackedLayoutBoxMaps(LayoutBox* descendant, TrackedDescendantsMap*&, TrackedContainerMap*&);
-    static void removeFromTrackedLayoutBoxMaps(LayoutBox* descendant, TrackedDescendantsMap*&, TrackedContainerMap*&);
-
     Node* nodeForHitTest() const;
 
     bool tryLayoutDoingPositionedMovementOnly();
@@ -484,6 +496,10 @@ protected:
 
     virtual bool canCollapseAnonymousBlockChild() const { return true; }
 
+    LayoutBlockRareData* layoutBlockRareData() const { return static_cast<LayoutBlockRareData*>(rareData()); }
+    LayoutBlockRareData& ensureLayoutBlockRareData() { return static_cast<LayoutBlockRareData&>(ensureRareData()); }
+    LayoutBoxRareData* createRareData() override { return new LayoutBlockRareData; }
+
     LayoutObjectChildList m_children;
     LineBoxList m_lineBoxes; // All of the root line boxes created for this block flow.  For example, <div>Hello<br>world.</div> will have two total lines for the <div>.