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diff --git a/Source/WTF/wtf/MonotonicTime.h b/Source/WTF/wtf/MonotonicTime.h
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+/*
+ * Copyright (C) 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:
+ * 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. ``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
+ * 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 WTF_MonotonicTime_h
+#define WTF_MonotonicTime_h
+
+#include <wtf/ClockType.h>
+#include <wtf/Seconds.h>
+
+namespace WTF {
+
+class WallTime;
+class PrintStream;
+
+// The current time according to a monotonic clock. Monotonic clocks don't go backwards and
+// possibly don't count downtime. This uses floating point internally so that you can reason about
+// infinity and other things that arise in math. It's acceptable to use this to wrap NaN times,
+// negative times, and infinite times, so long as they are all relative to the same clock.
+// Specifically, MonotonicTime should be used in agreement with the principle that
+// MonotonicTime::now().secondsSinceEpoch().value() is the same as
+// WTF::monotonicallyIncreasingTime().
+class MonotonicTime {
+public:
+    static const ClockType clockType = ClockType::Monotonic;
+    
+    // This is the epoch. So, x.secondsSinceEpoch() should be the same as x - MonotonicTime().
+    MonotonicTime() { }
+    
+    // Call this if you know for sure that the double represents time according to
+    // WTF::monotonicallyIncreasingTime(). It must be in seconds and it must be from the same time
+    // source.
+    static MonotonicTime fromRawSeconds(double value)
+    {
+        MonotonicTime result;
+        result.m_value = value;
+        return result;
+    }
+    
+    WTF_EXPORT_PRIVATE static MonotonicTime now();
+    
+    static MonotonicTime infinity() { return fromRawSeconds(std::numeric_limits<double>::infinity()); }
+
+    Seconds secondsSinceEpoch() const { return Seconds(m_value); }
+    
+    MonotonicTime approximateMonotonicTime() const { return *this; }
+    WTF_EXPORT_PRIVATE WallTime approximateWallTime() const;
+    
+    explicit operator bool() const { return !!m_value; }
+    
+    MonotonicTime operator+(Seconds other) const
+    {
+        return fromRawSeconds(m_value + other.value());
+    }
+    
+    MonotonicTime operator-(Seconds other) const
+    {
+        return fromRawSeconds(m_value - other.value());
+    }
+    
+    // Time is a scalar and scalars can be negated as this could arise from algebraic
+    // transformations. So, we allow it.
+    MonotonicTime operator-() const
+    {
+        return fromRawSeconds(-m_value);
+    }
+    
+    MonotonicTime operator+=(Seconds other)
+    {
+        return *this = *this + other;
+    }
+    
+    MonotonicTime operator-=(Seconds other)
+    {
+        return *this = *this - other;
+    }
+    
+    Seconds operator-(MonotonicTime other) const
+    {
+        return Seconds(m_value - other.m_value);
+    }
+    
+    bool operator==(MonotonicTime other) const
+    {
+        return m_value == other.m_value;
+    }
+    
+    bool operator!=(MonotonicTime other) const
+    {
+        return m_value != other.m_value;
+    }
+    
+    bool operator<(MonotonicTime other) const
+    {
+        return m_value < other.m_value;
+    }
+    
+    bool operator>(MonotonicTime other) const
+    {
+        return m_value > other.m_value;
+    }
+    
+    bool operator<=(MonotonicTime other) const
+    {
+        return m_value <= other.m_value;
+    }
+    
+    bool operator>=(MonotonicTime other) const
+    {
+        return m_value >= other.m_value;
+    }
+    
+    WTF_EXPORT_PRIVATE void dump(PrintStream&) const;
+
+private:
+    double m_value { 0 };
+};
+
+} // namespace WTF
+
+using WTF::MonotonicTime;
+
+#endif // WTF_MonotonicTime_h