Revert of Move smoothing filter to common audio.

webrtc/common_audio/smoothing_filter.h

Index: webrtc/common_audio/smoothing_filter.h
diff --git a/webrtc/common_audio/smoothing_filter.h b/webrtc/common_audio/smoothing_filter.h
deleted file mode 100644
index 30d8b7c87d9ef95e1e33f6e8f1ec3bfbff83b531..0000000000000000000000000000000000000000
--- a/webrtc/common_audio/smoothing_filter.h
+++ /dev/null
@@ -1,54 +0,0 @@
-/*
- *  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_COMMON_AUDIO_SMOOTHING_FILTER_H_
-#define WEBRTC_COMMON_AUDIO_SMOOTHING_FILTER_H_
-
-#include "webrtc/base/constructormagic.h"
-#include "webrtc/base/exp_filter.h"
-#include "webrtc/base/optional.h"
-#include "webrtc/system_wrappers/include/clock.h"
-
-namespace webrtc {
-
-class SmoothingFilter {
- public:
-  virtual ~SmoothingFilter() = default;
-  virtual void AddSample(float sample) = 0;
-  virtual rtc::Optional<float> GetAverage() const = 0;
-};
-
-// SmoothingFilterImpl applies an exponential filter
-//   alpha = exp(-sample_interval / time_constant);
-//   y[t] = alpha * y[t-1] + (1 - alpha) * sample;
-class SmoothingFilterImpl final : public SmoothingFilter {
- public:
-  // |time_constant_ms| is the time constant for the exponential filter.
-  SmoothingFilterImpl(int time_constant_ms, const Clock* clock);
-
-  void AddSample(float sample) override;
-  rtc::Optional<float> GetAverage() const override;
-
- private:
-  const int time_constant_ms_;
-  const Clock* const clock_;
-
-  bool first_sample_received_;
-  bool initialized_;
-  int64_t first_sample_time_ms_;
-  int64_t last_sample_time_ms_;
-  rtc::ExpFilter filter_;
-
-  RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(SmoothingFilterImpl);
-};
-
-}  // namespace webrtc
-
-#endif  // WEBRTC_COMMON_AUDIO_SMOOTHING_FILTER_H_