Adding the ability to use a simulated clock for unit tests.

webrtc/base/fakeclock.h

Index: webrtc/base/fakeclock.h
diff --git a/webrtc/base/fakeclock.h b/webrtc/base/fakeclock.h
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+/*
+ *  Copyright 2016 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef WEBRTC_BASE_FAKECLOCK_H_
+#define WEBRTC_BASE_FAKECLOCK_H_
+
+#include "webrtc/base/criticalsection.h"
+#include "webrtc/base/timedelta.h"
+#include "webrtc/base/timeutils.h"
+
+namespace rtc {
+
+// Fake clock for use with unit tests, which does not tick on its own.
+// Starts at time 0.
+class FakeClock : public ClockInterface {
+ public:
+  ~FakeClock() override {}
+
+  // ClockInterface implementation.
+  uint64_t TimeNanos() const override;
+
+  // Methods that can be used by the test to control the time.
+
+  // Should only be used to set a time in the future.
+  void SetTimeNanos(uint64_t nanos);
+
+  void AdvanceTime(TimeDelta delta);
+
+ private:
+  CriticalSection lock_;
+  uint64_t time_ GUARDED_BY(lock_) = 0u;
+};
+
+}  // namespace rtc
+
+#endif  // WEBRTC_BASE_FAKECLOCK_H_