Prioritizing input and compositor tasks in the blink scheduler.

Source/wtf/DoubleBufferedDeque.h

Index: Source/wtf/DoubleBufferedDeque.h
diff --git a/Source/wtf/DoubleBufferedDeque.h b/Source/wtf/DoubleBufferedDeque.h
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+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef DoubleBufferedDeque_h
+#define DoubleBufferedDeque_h
+
+#include "wtf/Deque.h"
+#include "wtf/Noncopyable.h"
+
+namespace WTF {
+
+// A helper class for managing double buffered deques, typically where the client locks when appending or swapping.
+template <typename T> class DoubleBufferedDeque {
+    WTF_MAKE_NONCOPYABLE(DoubleBufferedDeque);
+public:
+    DoubleBufferedDeque()
+        : m_activeIndex(0) { }
+
+    void append(const T& value)
+    {
+        m_queue[m_activeIndex].append(value);
+    }
+
+    bool isEmpty() const
+    {
+        return m_queue[m_activeIndex].isEmpty();
+    }
+
+    Deque<T>& swapBuffers()
+    {
+        int oldIndex = m_activeIndex;
+        m_activeIndex ^= 1;
+        ASSERT(m_queue[m_activeIndex].isEmpty());
+        return m_queue[oldIndex];
+    }
+
+private:
+    Deque<T> m_queue[2];
+    int m_activeIndex;
+};
+
+} // namespace WTF
+
+using WTF::DoubleBufferedDeque;
+
+#endif // DoubleBufferedDeque_h