Added first layer of the echo canceller 3 functionality

webrtc/modules/audio_processing/aec3/cascaded_biquad_filter.h

Index: webrtc/modules/audio_processing/aec3/cascaded_biquad_filter.h
diff --git a/webrtc/modules/audio_processing/aec3/cascaded_biquad_filter.h b/webrtc/modules/audio_processing/aec3/cascaded_biquad_filter.h
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index 0000000000000000000000000000000000000000..438a166eae0094451d39aa85166061900fff59e3
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+++ b/webrtc/modules/audio_processing/aec3/cascaded_biquad_filter.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_MODULES_AUDIO_PROCESSING_AEC3_CASCADED_BIQUAD_FILTER_H_
+#define WEBRTC_MODULES_AUDIO_PROCESSING_AEC3_CASCADED_BIQUAD_FILTER_H_
+
+#include <vector>
+
+#include "webrtc/base/array_view.h"
+#include "webrtc/base/constructormagic.h"
+
+namespace webrtc {
+
+// Applies a number of identical biquads in a cascaded manner. The filter
+// implementation is direct form 1.
+class CascadedBiQuadFilter {
+ public:
+  struct BiQuadState {
+    BiQuadState() : x(), y() {}
+    float x[2];
+    float y[2];
+  };
+
+  struct BiQuadCoefficients {
+    float b[3];
+    float a[2];
+  };
+
+  CascadedBiQuadFilter(
+      const CascadedBiQuadFilter::BiQuadCoefficients& coefficients,
+      size_t num_biquads);
+  ~CascadedBiQuadFilter();
+  // Applies the biquads on the values in x in order to form the output in y.
+  void Process(rtc::ArrayView<const float> x, rtc::ArrayView<float> y);
+  // Applies the biquads on the values in y in an in-place manner.
+  void Process(rtc::ArrayView<float> y);
+
+ private:
+  void ApplyBiQuad(rtc::ArrayView<const float> x,
+                   rtc::ArrayView<float> y,
+                   CascadedBiQuadFilter::BiQuadState* biquad_state);
+
+  std::vector<BiQuadState> biquad_states_;
+  const BiQuadCoefficients coefficients_;
+
+  RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(CascadedBiQuadFilter);
+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_MODULES_AUDIO_PROCESSING_AEC3_CASCADED_BIQUAD_FILTER_H_