Added A/V sync tests with drifting clocks.

webrtc/test/drifting_clock.h

Index: webrtc/test/drifting_clock.h
diff --git a/webrtc/test/drifting_clock.h b/webrtc/test/drifting_clock.h
new file mode 100644
index 0000000000000000000000000000000000000000..d434186d7d0aad0bc43787bab96f8e0150d043c3
--- /dev/null
+++ b/webrtc/test/drifting_clock.h
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+/*
+ *  Copyright (c) 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_TEST_DRIFTING_CLOCK_H_
+#define WEBRTC_TEST_DRIFTING_CLOCK_H_
+
+#include "webrtc/system_wrappers/include/clock.h"
+
+namespace webrtc {
+namespace test {
+class DriftingClock : public Clock {
+ public:
+  // TODO(danilchap): Make this constants constexpr when it would be supported.
+  static const float kDoubleSpeed;  // 2.0f;
+  static const float kNoDrift;      // 1.0f;
+  static const float kHalfSpeed;    // 0.5f;
+
+  DriftingClock(Clock* clock, float speed);
+
+  // TODO(danilchap): Make this functions constexpr when it would be supported.
+  static float PercentsFaster(float percent) { return 1.0f + percent / 100.0f; }
+  static float PercentsSlower(float percent) { return 1.0f - percent / 100.0f; }
+
+  int64_t TimeInMilliseconds() const override;
+  int64_t TimeInMicroseconds() const override;
+  void CurrentNtp(uint32_t& seconds, uint32_t& fractions) const override;
+  int64_t CurrentNtpInMilliseconds() const override;
+
+ private:
+  float Drift() const;
+
+  Clock* const clock_;
+  const float drift_;
+  const int64_t start_time_;
+};
+}  // namespace test
+}  // namespace webrtc
+
+#endif  // WEBRTC_TEST_DRIFTING_CLOCK_H_