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diff --git a/Source/JavaScriptCore/runtime/StringRecursionChecker.h b/Source/JavaScriptCore/runtime/StringRecursionChecker.h
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+++ b/Source/JavaScriptCore/runtime/StringRecursionChecker.h
@@ -0,0 +1,79 @@
+/*
+ *  Copyright (C) 2011 Apple Inc. All rights reserved.
+ *
+ *  This library is free software; you can redistribute it and/or
+ *  modify it under the terms of the GNU Lesser General Public
+ *  License as published by the Free Software Foundation; either
+ *  version 2 of the License, or (at your option) any later version.
+ *
+ *  This library is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ *  Lesser General Public License for more details.
+ *
+ *  You should have received a copy of the GNU Lesser General Public
+ *  License along with this library; if not, write to the Free Software
+ *  Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
+ *
+ */
+
+#ifndef StringRecursionChecker_h
+#define StringRecursionChecker_h
+
+#include "Interpreter.h"
+
+namespace JSC {
+
+class StringRecursionChecker {
+    WTF_MAKE_NONCOPYABLE(StringRecursionChecker);
+
+public:
+    StringRecursionChecker(ExecState*, JSObject* thisObject);
+    ~StringRecursionChecker();
+
+    EncodedJSValue earlyReturnValue() const; // 0 if everything is OK, value to return for failure cases
+
+private:
+    EncodedJSValue throwStackOverflowError();
+    EncodedJSValue emptyString();
+    EncodedJSValue performCheck();
+
+    ExecState* m_exec;
+    JSObject* m_thisObject;
+    EncodedJSValue m_earlyReturnValue;
+};
+
+inline EncodedJSValue StringRecursionChecker::performCheck()
+{
+    int size = m_exec->globalData().stringRecursionCheckVisitedObjects.size();
+    if (size >= MaxSmallThreadReentryDepth && size >= m_exec->globalData().maxReentryDepth)
+        return throwStackOverflowError();
+    bool alreadyVisited = !m_exec->globalData().stringRecursionCheckVisitedObjects.add(m_thisObject).second;
+    if (alreadyVisited)
+        return emptyString(); // Return empty string to avoid infinite recursion.
+    return 0; // Indicate success.
+}
+
+inline StringRecursionChecker::StringRecursionChecker(ExecState* exec, JSObject* thisObject)
+    : m_exec(exec)
+    , m_thisObject(thisObject)
+    , m_earlyReturnValue(performCheck())
+{
+}
+
+inline EncodedJSValue StringRecursionChecker::earlyReturnValue() const
+{
+    return m_earlyReturnValue;
+}
+
+inline StringRecursionChecker::~StringRecursionChecker()
+{
+    if (m_earlyReturnValue)
+        return;
+    ASSERT(m_exec->globalData().stringRecursionCheckVisitedObjects.contains(m_thisObject));
+    m_exec->globalData().stringRecursionCheckVisitedObjects.remove(m_thisObject);
+}
+
+}
+
+#endif