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diff --git a/Source/JavaScriptCore/runtime/WeakGCMap.h b/Source/JavaScriptCore/runtime/WeakGCMap.h
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+/*
+ * Copyright (C) 2009, 2015 Apple 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:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS''
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+ * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS
+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF
+ * THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef WeakGCMap_h
+#define WeakGCMap_h
+
+#include "Weak.h"
+#include "WeakInlines.h"
+#include <wtf/HashMap.h>
+
+namespace JSC {
+
+// A HashMap with Weak<JSCell> values, which automatically removes values once they're garbage collected.
+
+template<typename KeyArg, typename ValueArg, typename HashArg = typename DefaultHash<KeyArg>::Hash,
+    typename KeyTraitsArg = HashTraits<KeyArg>>
+class WeakGCMap {
+    WTF_MAKE_FAST_ALLOCATED;
+    typedef Weak<ValueArg> ValueType;
+    typedef HashMap<KeyArg, ValueType, HashArg, KeyTraitsArg> HashMapType;
+
+public:
+    typedef typename HashMapType::KeyType KeyType;
+    typedef typename HashMapType::AddResult AddResult;
+    typedef typename HashMapType::iterator iterator;
+    typedef typename HashMapType::const_iterator const_iterator;
+
+    explicit WeakGCMap(VM&);
+    ~WeakGCMap();
+
+    ValueArg* get(const KeyType& key) const
+    {
+        return m_map.get(key);
+    }
+
+    AddResult set(const KeyType& key, ValueType value)
+    {
+        return m_map.set(key, WTF::move(value));
+    }
+
+    bool remove(const KeyType& key)
+    {
+        return m_map.remove(key);
+    }
+
+    void clear()
+    {
+        m_map.clear();
+    }
+
+    bool isEmpty() const
+    {
+        const_iterator it = m_map.begin();
+        const_iterator end = m_map.end();
+        while (it != end) {
+            if (it->value)
+                return true;
+        }
+        return false;
+    }
+
+    iterator find(const KeyType& key)
+    {
+        iterator it = m_map.find(key);
+        iterator end = m_map.end();
+        if (it != end && !it->value) // Found a zombie value.
+            return end;
+        return it;
+    }
+
+    const_iterator find(const KeyType& key) const
+    {
+        return const_cast<WeakGCMap*>(this)->find(key);
+    }
+
+    template<typename Functor>
+    void forEach(Functor functor)
+    {
+        for (auto& pair : m_map) {
+            if (pair.value)
+                functor(pair.key, pair.value.get());
+        }
+    }
+
+    bool contains(const KeyType& key) const
+    {
+        return find(key) != m_map.end();
+    }
+
+    void pruneStaleEntries();
+
+private:
+    HashMapType m_map;
+    VM& m_vm;
+};
+
+} // namespace JSC
+
+#endif // WeakGCMap_h