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diff --git a/Source/WTF/wtf/CrossThreadCopier.h b/Source/WTF/wtf/CrossThreadCopier.h
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+++ b/Source/WTF/wtf/CrossThreadCopier.h
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+/*
+ * Copyright (C) 2009, 2010 Google Inc. All rights reserved.
+ * Copyright (C) 2014, 2015, 2016 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:
+ *
+ *     * 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
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND 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 THE COPYRIGHT
+ * OWNER 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.
+ */
+
+#pragma once
+
+#include <wtf/Assertions.h>
+#include <wtf/Forward.h>
+#include <wtf/PassRefPtr.h>
+#include <wtf/RefPtr.h>
+#include <wtf/Threading.h>
+#include <wtf/text/WTFString.h>
+
+namespace WTF {
+
+struct CrossThreadCopierBaseHelper {
+    template<typename T> struct RemovePointer {
+        typedef T Type;
+    };
+    template<typename T> struct RemovePointer<T*> {
+        typedef T Type;
+    };
+
+    template<typename T> struct RemovePointer<RefPtr<T>> {
+        typedef T Type;
+    };
+
+    template<typename T> struct RemovePointer<PassRefPtr<T>> {
+        typedef T Type;
+    };
+
+    template<typename T> struct IsEnumOrConvertibleToInteger {
+        static const bool value = std::is_integral<T>::value || std::is_enum<T>::value || std::is_convertible<T, long double>::value;
+    };
+
+    template<typename T> struct IsThreadSafeRefCountedPointer {
+        static const bool value = std::is_convertible<typename RemovePointer<T>::Type*, ThreadSafeRefCounted<typename RemovePointer<T>::Type>*>::value;
+    };
+};
+
+template<typename T> struct CrossThreadCopierPassThrough {
+    typedef T Type;
+    static Type copy(const T& parameter)
+    {
+        return parameter;
+    }
+};
+
+template<bool isEnumOrConvertibleToInteger, bool isThreadSafeRefCounted, typename T> struct CrossThreadCopierBase;
+
+// Integers get passed through without any changes.
+template<typename T> struct CrossThreadCopierBase<true, false, T> : public CrossThreadCopierPassThrough<T> {
+};
+
+// Classes that have an isolatedCopy() method get a default specialization.
+template<class T> struct CrossThreadCopierBase<false, false, T> {
+    static T copy(const T& value)
+    {
+        return value.isolatedCopy();
+    }
+};
+
+// Custom copy methods.
+template<typename T> struct CrossThreadCopierBase<false, true, T> {
+    typedef typename CrossThreadCopierBaseHelper::RemovePointer<T>::Type RefCountedType;
+    static_assert(std::is_convertible<RefCountedType*, ThreadSafeRefCounted<RefCountedType>*>::value, "T is not convertible to ThreadSafeRefCounted!");
+
+    typedef PassRefPtr<RefCountedType> Type;
+    static Type copy(const T& refPtr)
+    {
+        return refPtr;
+    }
+};
+
+template<> struct CrossThreadCopierBase<false, false, std::chrono::system_clock::time_point> {
+    typedef std::chrono::system_clock::time_point Type;
+    static Type copy(const Type& source)
+    {
+        return source;
+    }
+};
+
+template<> struct CrossThreadCopierBase<false, false, WTF::ASCIILiteral> {
+    typedef WTF::ASCIILiteral Type;
+    static Type copy(const Type& source)
+    {
+        return source;
+    }
+};
+
+template<typename T>
+struct CrossThreadCopier : public CrossThreadCopierBase<CrossThreadCopierBaseHelper::IsEnumOrConvertibleToInteger<T>::value, CrossThreadCopierBaseHelper::IsThreadSafeRefCountedPointer<T>::value, T> {
+};
+
+// Default specialization for Vectors of CrossThreadCopyable classes.
+template<typename T> struct CrossThreadCopierBase<false, false, Vector<T>> {
+    typedef Vector<T> Type;
+    static Type copy(const Type& source)
+    {
+        Type destination;
+        destination.reserveInitialCapacity(source.size());
+        for (auto& object : source)
+            destination.uncheckedAppend(CrossThreadCopier<T>::copy(object));
+        return destination;
+    }
+};
+
+} // namespace WTF
+
+using WTF::CrossThreadCopierBaseHelper;
+using WTF::CrossThreadCopierBase;
+using WTF::CrossThreadCopier;