Adds missing file

EyeRecToo/src/MonotonicClock.h

+#ifndef MONOTONICCLOCK_H
+#define MONOTONICCLOCK_H
+
+#include <chrono>
+
+using Timestamp = double;
+using SteadyTimePoint = std::chrono::time_point<std::chrono::steady_clock>;
+
+class MonotonicClock {
+public:
+    MonotonicClock()
+        : started(now())
+    {
+    }
+
+    static SteadyTimePoint now() { return std::chrono::steady_clock::now(); }
+
+    Timestamp elapsed() const
+    {
+        return 1e-6 * std::chrono::duration_cast<std::chrono::nanoseconds>(now() - started).count();
+    }
+
+    Timestamp elapsed(const SteadyTimePoint& p) const
+    {
+        return 1e-6 * std::chrono::duration_cast<std::chrono::nanoseconds>(p - started).count();
+    }
+
+private:
+    const SteadyTimePoint started;
+};
+
+using ReferenceClock = MonotonicClock;
+
+#endif // MONOTONICCLOCK_H