Added a new echo likelihood stat that reports the maximum value from a previous time period.

webrtc/modules/audio_processing/echo_detector/moving_max.h

Index: webrtc/modules/audio_processing/echo_detector/moving_max.h
diff --git a/webrtc/modules/audio_processing/echo_detector/moving_max.h b/webrtc/modules/audio_processing/echo_detector/moving_max.h
new file mode 100644
index 0000000000000000000000000000000000000000..556facfad41274b120fbe73a339241d7c8264a75
--- /dev/null
+++ b/webrtc/modules/audio_processing/echo_detector/moving_max.h
@@ -0,0 +1,36 @@
+/*
+ *  Copyright (c) 2017 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_ECHO_DETECTOR_MOVING_MAX_H_
+#define WEBRTC_MODULES_AUDIO_PROCESSING_ECHO_DETECTOR_MOVING_MAX_H_
+
+#include <stddef.h>
+
+namespace webrtc {
+
+class MovingMax {
+ public:
+  explicit MovingMax(size_t window_size);
+  ~MovingMax();
+
+  void Update(float value);
+  float max() const;
+  // Reset all of the state in this class.
+  void Clear();
+
+ private:
+  float max_value_ = 0.f;
+  size_t counter_ = 0;
+  size_t window_size_ = 1;
+};
+
+}  // namespace webrtc
+
+#endif  // WEBRTC_MODULES_AUDIO_PROCESSING_ECHO_DETECTOR_MOVING_MAX_H_