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diff --git a/Source/WebKit2/Shared/API/APIClient.h b/Source/WebKit2/Shared/API/APIClient.h
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+/*
+ * Copyright (C) 2010 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 APIClient_h
+#define APIClient_h
+
+#include <algorithm>
+#include <array>
+
+namespace API {
+
+template<typename ClientInterface> struct ClientTraits;
+
+template<typename ClientInterface> class Client {
+    typedef typename ClientTraits<ClientInterface>::Versions ClientVersions;
+    static const int latestClientVersion = std::tuple_size<ClientVersions>::value - 1;
+    typedef typename std::tuple_element<latestClientVersion, ClientVersions>::type LatestClientInterface;
+
+    // Helper class that can return an std::array of element sizes in a tuple.
+    template<typename> struct InterfaceSizes;
+    template<typename... Interfaces> struct InterfaceSizes<std::tuple<Interfaces...>> {
+        static std::array<size_t, sizeof...(Interfaces)> sizes()
+        {
+            return { { sizeof(Interfaces)... } };
+        }
+    };
+
+public:
+    Client()
+    {
+#if !ASSERT_DISABLED
+        auto interfaceSizes = InterfaceSizes<ClientVersions>::sizes();
+        ASSERT(std::is_sorted(interfaceSizes.begin(), interfaceSizes.end()));
+#endif
+
+        initialize(nullptr);
+    }
+
+    void initialize(const ClientInterface* client)
+    {
+        if (client && client->version == latestClientVersion) {
+            m_client = *reinterpret_cast<const LatestClientInterface*>(client);
+            return;
+        }
+
+        memset(&m_client, 0, sizeof(m_client));
+
+        if (client && client->version < latestClientVersion) {
+            auto interfaceSizes = InterfaceSizes<ClientVersions>::sizes();
+
+            memcpy(&m_client, client, interfaceSizes[client->version]);
+        }
+    }
+
+    const LatestClientInterface& client() const { return m_client; }
+
+protected:
+    LatestClientInterface m_client;
+};
+
+} // namespace API
+
+#endif // APIClient_h