Add algorithm for Residual Echo Detector.

webrtc/modules/audio_processing/BUILD.gn

Index: webrtc/modules/audio_processing/BUILD.gn
diff --git a/webrtc/modules/audio_processing/BUILD.gn b/webrtc/modules/audio_processing/BUILD.gn
index 7647161406013ff7ee59249d4e99dd21b8152fd5..68f0378e542f920f82ff8c005704c5982d8c5d03 100644
--- a/webrtc/modules/audio_processing/BUILD.gn
+++ b/webrtc/modules/audio_processing/BUILD.gn
@@ -61,8 +61,16 @@ rtc_static_library("audio_processing") {
     "echo_cancellation_impl.h",
     "echo_control_mobile_impl.cc",
     "echo_control_mobile_impl.h",
+    "echo_detector/circular_buffer.cc",
+    "echo_detector/circular_buffer.h",
     "echo_detector/echo_detector.cc",
     "echo_detector/echo_detector.h",
+    "echo_detector/mean_variance_estimator.cc",
+    "echo_detector/mean_variance_estimator.h",
+    "echo_detector/normalized_covariance_estimator.cc",
+    "echo_detector/normalized_covariance_estimator.h",
+    "echo_detector/sliding_window_minimum.cc",
+    "echo_detector/sliding_window_minimum.h",
     "gain_control_for_experimental_agc.cc",
     "gain_control_for_experimental_agc.h",
     "gain_control_impl.cc",