Introduced the new parameter setting scheme for activating the high-pass filter in APM

webrtc/modules/audio_processing/low_cut_filter.h

Index: webrtc/modules/audio_processing/low_cut_filter.h
diff --git a/webrtc/modules/audio_processing/low_cut_filter.h b/webrtc/modules/audio_processing/low_cut_filter.h
new file mode 100644
index 0000000000000000000000000000000000000000..3a4da71d8b7a92b1d99e75bb5e71c51a59e50aeb
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+++ b/webrtc/modules/audio_processing/low_cut_filter.h
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+/*
+ *  Copyright (c) 2012 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_MODULES_AUDIO_PROCESSING_LOW_CUT_FILTER_H_
+#define WEBRTC_MODULES_AUDIO_PROCESSING_LOW_CUT_FILTER_H_
+
+#include <memory>
+#include <vector>
+
+#include "webrtc/base/constructormagic.h"
+
+namespace webrtc {
+
+class AudioBuffer;
+
+class LowCutFilter {
+ public:
+  LowCutFilter(size_t channels, int sample_rate_hz);
+  ~LowCutFilter();
+  void Process(AudioBuffer* audio);
+
+ private:
+  class BiquadFilter;
+  std::vector<std::unique_ptr<BiquadFilter>> filters_;
+  RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(LowCutFilter);
+};
+}  // namespace webrtc
+
+#endif  // WEBRTC_MODULES_AUDIO_PROCESSING_LOW_CUT_FILTER_H_