Add a placeholder stat for logging the estimated residual echo likelihood.

webrtc/audio/audio_send_stream.cc

Index: webrtc/audio/audio_send_stream.cc
diff --git a/webrtc/audio/audio_send_stream.cc b/webrtc/audio/audio_send_stream.cc
index ee84b96aaa3700a8e7d937e0cf3d4ec1dfd0990d..52b07435efc331727ca887f4c7039741abe93ff6 100644
--- a/webrtc/audio/audio_send_stream.cc
+++ b/webrtc/audio/audio_send_stream.cc
@@ -236,6 +236,9 @@ webrtc::AudioSendStream::Stats AudioSendStream::GetStats() const {
     stats.echo_return_loss_enhancement = erle;
   }
 
+  // TODO(ivoc): Hook this up to the residual echo detector.
+  stats.residual_echo_likelihood = 0.0f;
+
   internal::AudioState* audio_state =
       static_cast<internal::AudioState*>(audio_state_.get());
   stats.typing_noise_detected = audio_state->typing_noise_detected();