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diff --git a/Source/WebCore/page/scrolling/ScrollingThread.h b/Source/WebCore/page/scrolling/ScrollingThread.h
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+++ b/Source/WebCore/page/scrolling/ScrollingThread.h
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+/*
+ * Copyright (C) 2012, 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.
+ */
+
+#pragma once
+
+#if ENABLE(ASYNC_SCROLLING)
+
+#include <functional>
+#include <wtf/Condition.h>
+#include <wtf/Forward.h>
+#include <wtf/Function.h>
+#include <wtf/Lock.h>
+#include <wtf/Noncopyable.h>
+#include <wtf/Threading.h>
+#include <wtf/Vector.h>
+
+#if PLATFORM(COCOA)
+#include <wtf/RetainPtr.h>
+#endif
+
+namespace WebCore {
+
+class ScrollingThread {
+    WTF_MAKE_NONCOPYABLE(ScrollingThread);
+
+public:
+    static bool isCurrentThread();
+    WEBCORE_EXPORT static void dispatch(Function<void ()>&&);
+
+    // Will dispatch the given function on the main thread once all pending functions
+    // on the scrolling thread have finished executing. Used for synchronization purposes.
+    WEBCORE_EXPORT static void dispatchBarrier(Function<void ()>&&);
+
+private:
+    friend NeverDestroyed<ScrollingThread>;
+
+    ScrollingThread();
+
+    static ScrollingThread& singleton();
+
+    void createThreadIfNeeded();
+    static void threadCallback(void* scrollingThread);
+    void threadBody();
+    void dispatchFunctionsFromScrollingThread();
+
+    void initializeRunLoop();
+    void wakeUpRunLoop();
+
+#if PLATFORM(COCOA)
+    static void threadRunLoopSourceCallback(void* scrollingThread);
+    void threadRunLoopSourceCallback();
+#endif
+
+    ThreadIdentifier m_threadIdentifier;
+
+    Condition m_initializeRunLoopConditionVariable;
+    Lock m_initializeRunLoopMutex;
+
+    Lock m_functionsMutex;
+    Vector<Function<void ()>> m_functions;
+
+#if PLATFORM(COCOA)
+    // FIXME: We should use WebCore::RunLoop here.
+    RetainPtr<CFRunLoopRef> m_threadRunLoop;
+    RetainPtr<CFRunLoopSourceRef> m_threadRunLoopSource;
+#endif
+};
+
+} // namespace WebCore
+
+#endif // ENABLE(ASYNC_SCROLLING)