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diff --git a/Source/JavaScriptCore/runtime/ScopedArgumentsTable.h b/Source/JavaScriptCore/runtime/ScopedArgumentsTable.h
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+++ b/Source/JavaScriptCore/runtime/ScopedArgumentsTable.h
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+/*
+ * Copyright (C) 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. ``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
+ * 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 ScopedArgumentsTable_h
+#define ScopedArgumentsTable_h
+
+#include "JSCell.h"
+#include "ScopeOffset.h"
+#include <wtf/Assertions.h>
+
+namespace JSC {
+
+// This class's only job is to hold onto the list of ScopeOffsets for each argument that a
+// function has. Most of the time, the BytecodeGenerator will create one of these and it will
+// never be modified subsequently. There is a rare case where a ScopedArguments object is created
+// and aliases one of these and then decides to modify it; in that case we do copy-on-write. This
+// makes sense because such modifications are so uncommon. You'd have to do something crazy like
+// "delete arguments[i]" or some variant of defineOwnProperty.
+class ScopedArgumentsTable final : public JSCell {
+public:
+    typedef JSCell Base;
+    static const unsigned StructureFlags = Base::StructureFlags | StructureIsImmortal;
+    
+private:
+    ScopedArgumentsTable(VM&);
+    ~ScopedArgumentsTable();
+
+public:
+    static ScopedArgumentsTable* create(VM&);
+    static ScopedArgumentsTable* create(VM&, uint32_t length);
+    
+    static const bool needsDestruction = true;
+    static void destroy(JSCell*);
+
+    ScopedArgumentsTable* clone(VM&);
+    
+    uint32_t length() const { return m_length; }
+    ScopedArgumentsTable* setLength(VM&, uint32_t newLength);
+    
+    ScopeOffset get(uint32_t i) const
+    {
+        return const_cast<ScopedArgumentsTable*>(this)->at(i);
+    }
+    
+    void lock()
+    {
+        m_locked = true;
+    }
+    
+    ScopedArgumentsTable* set(VM&, uint32_t index, ScopeOffset);
+    
+    DECLARE_INFO;
+    
+    static Structure* createStructure(VM&, JSGlobalObject*, JSValue prototype);
+
+    static ptrdiff_t offsetOfLength() { return OBJECT_OFFSETOF(ScopedArgumentsTable, m_length); }
+    static ptrdiff_t offsetOfArguments() { return OBJECT_OFFSETOF(ScopedArgumentsTable, m_arguments); }
+
+private:
+    ScopeOffset& at(uint32_t i)
+    {
+        ASSERT_WITH_SECURITY_IMPLICATION(i < m_length);
+        return m_arguments[i];
+    }
+    
+    uint32_t m_length;
+    bool m_locked; // Being locked means that there are multiple references to this object and none of them expect to see the others' modifications. This means that modifications need to make a copy first.
+    std::unique_ptr<ScopeOffset[]> m_arguments;
+};
+
+} // namespace JSC
+
+#endif // ScopedArgumentsTable_h
+