Adds fuzzer for the residual echo detector.

webrtc/modules/audio_processing/residual_echo_detector.cc

Index: webrtc/modules/audio_processing/residual_echo_detector.cc
diff --git a/webrtc/modules/audio_processing/residual_echo_detector.cc b/webrtc/modules/audio_processing/residual_echo_detector.cc
index e95e0894bfc5d8f735243c8fdd4d6673cfba349f..e25d52899a431e0688a746868208e253a1f4062e 100644
--- a/webrtc/modules/audio_processing/residual_echo_detector.cc
+++ b/webrtc/modules/audio_processing/residual_echo_detector.cc
@@ -104,6 +104,7 @@ void ResidualEchoDetector::AnalyzeCaptureAudio(
     echo_likelihood_ = std::max(
         echo_likelihood_, covariances_[delay].normalized_cross_correlation());
   }
+  RTC_DCHECK_LT(echo_likelihood_, 1.1f);
   reliability_ = (1.0f - kAlpha) * reliability_ + kAlpha * 1.0f;
   echo_likelihood_ *= reliability_;
   // This is a temporary fix to prevent echo likelihood values > 1.0.