Allow extracting the linear AEC output

This CL enables extracting the linear AEC output,
allowing for more straightforward
testing/development.

Bug: b/140823178
Change-Id: I14f7934008d87066b35500466cb6e6d96f811688
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/153672
Commit-Queue: Per Åhgren <peah@webrtc.org>
Reviewed-by: Gustaf Ullberg <gustaf@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#29789}
diff --git a/modules/audio_processing/aec3/echo_remover.h b/modules/audio_processing/aec3/echo_remover.h
index 6098a68..ef41646 100644
--- a/modules/audio_processing/aec3/echo_remover.h
+++ b/modules/audio_processing/aec3/echo_remover.h
@@ -42,6 +42,7 @@
       bool capture_signal_saturation,
       const absl::optional<DelayEstimate>& external_delay,
       RenderBuffer* render_buffer,
+      std::vector<std::vector<std::vector<float>>>* linear_output,
       std::vector<std::vector<std::vector<float>>>* capture) = 0;
 
   // Updates the status on whether echo leakage is detected in the output of the