Add missing header (for unique_ptr).

Bug: None
Change-Id: I2ee004ac4feca9a0c25551fc1709069e8df836b4
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/229026
Reviewed-by: Per Åhgren <peah@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#34783}

modules/audio_processing/aec3/reverb_model_estimator.h

@@ -12,6 +12,7 @@
 #define MODULES_AUDIO_PROCESSING_AEC3_REVERB_MODEL_ESTIMATOR_H_
 
 #include <array>
+#include <memory>
 #include <vector>
 
 #include "absl/types/optional.h"