Setting up OrderIterator shouldn't require an extra Vector

Source/core/rendering/OrderIterator.h

 /*
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 23 matching lines @@
 #include "wtf/Noncopyable.h"
 #include "wtf/Vector.h"
 
 namespace WebCore {
 
 class RenderBox;
 
 class OrderIterator {
     WTF_MAKE_NONCOPYABLE(OrderIterator);
 public:
+    friend class OrderIteratorPopulator;
+
     OrderIterator(const RenderBox*);
 
-    void setOrderValues(Vector<int>&);
     RenderBox* currentChild() const { return m_currentChild; }
     RenderBox* first();
     RenderBox* next();
     void reset();
 
 private:
     const RenderBox* m_containerBox;
     RenderBox* m_currentChild;
-    Vector<int> m_orderValues;
+    // The inline capacity for a single item is used to cover the most
+    // common case by far: if we only have the default 'order' value 0.
+    typedef Vector<int, 1> OrderValues;
+    OrderValues m_orderValues;
     Vector<int>::const_iterator m_orderValuesIterator;
 };
 
+class OrderIteratorPopulator {
+public:
+    OrderIteratorPopulator(OrderIterator& iterator)
+        : m_iterator(iterator)
+        , m_anyChildHasDefaultOrderValue(false)
+    {
+        // Note that we don't release the memory here, we only invalidate the size.
+        // This avoids unneeded reallocation if the size ends up not changing.
+        m_iterator.m_orderValues.shrink(0);
+    }
+
+    ~OrderIteratorPopulator();
+
+    void collectChild(const RenderBox*);
+
+private:
+    void removeDuplicatedOrderValues();
+
+    OrderIterator& m_iterator;
+    bool m_anyChildHasDefaultOrderValue;
+};
+
 } // namespace WebCore
 
 #endif //  OrderIterator_h