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diff --git a/dom/media/webaudio/blink/IIRFilter.h b/dom/media/webaudio/blink/IIRFilter.h
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+++ b/dom/media/webaudio/blink/IIRFilter.h
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+// Copyright 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef IIRFilter_h
+#define IIRFilter_h
+
+#include "nsTArray.h"
+
+typedef nsTArray<double> AudioDoubleArray;
+
+namespace blink {
+
+class IIRFilter final {
+ public:
+  // The maximum IIR filter order.  This also limits the number of feedforward
+  // coefficients.  The maximum number of coefficients is 20 according to the
+  // spec.
+  const static size_t kMaxOrder = 19;
+  IIRFilter(const AudioDoubleArray* feedforwardCoef,
+            const AudioDoubleArray* feedbackCoef);
+  ~IIRFilter();
+
+  void process(const float* sourceP, float* destP, size_t framesToProcess);
+
+  void reset();
+
+  void getFrequencyResponse(int nFrequencies, const float* frequency,
+                            float* magResponse, float* phaseResponse);
+
+  bool buffersAreZero();
+
+ private:
+  // Filter memory
+  //
+  // For simplicity, we assume |m_xBuffer| and |m_yBuffer| have the same length,
+  // and the length is a power of two.  Since the number of coefficients has a
+  // fixed upper length, the size of xBuffer and yBuffer is fixed. |m_xBuffer|
+  // holds the old input values and |m_yBuffer| holds the old output values
+  // needed to compute the new output value.
+  //
+  // m_yBuffer[m_bufferIndex] holds the most recent output value, say, y[n].
+  // Then m_yBuffer[m_bufferIndex - k] is y[n - k].  Similarly for m_xBuffer.
+  //
+  // To minimize roundoff, these arrays are double's instead of floats.
+  AudioDoubleArray m_xBuffer;
+  AudioDoubleArray m_yBuffer;
+
+  // Index into the xBuffer and yBuffer arrays where the most current x and y
+  // values should be stored.  xBuffer[bufferIndex] corresponds to x[n], the
+  // current x input value and yBuffer[bufferIndex] is where y[n], the current
+  // output value.
+  int m_bufferIndex;
+
+  // Coefficients of the IIR filter.
+  const AudioDoubleArray* m_feedback;
+  const AudioDoubleArray* m_feedforward;
+};
+
+}  // namespace blink
+
+#endif  // IIRFilter_h