Add AnalogGainStatsReporter to compute and report analog gain statistics

Implement AnalogGainStatsReporter and add it in AudioProcessingImpl.
This class computes statistics for analog gain updates and
periodically reports them into a histogram.

The added histograms for analog gain update statistics:

 - WebRTC.Audio.ApmAnalogGainDecreaseRate
 - WebRTC.Audio.ApmAnalogGainIncreaseRate
 - WebRTC.Audio.ApmAnalogGainUpdateRate
 - WebRTC.Audio.ApmAnalogGainDecreaseAverage
 - WebRTC.Audio.ApmAnalogGainIncreaseAverage
 - WebRTC.Audio.ApmAnalogGainUpdateAverage

The histograms are defined in
https://chromium-review.googlesource.com/c/chromium/src/+/3207987

Bug: webrtc:12774
Change-Id: I3c58d4bb3eb034a11c3f39ab8edb2bc67c5fd5e4
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/234140
Commit-Queue: Hanna Silen <silen@webrtc.org>
Reviewed-by: Per Ã…hgren <peah@webrtc.org>
Reviewed-by: Alessio Bazzica <alessiob@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#35301}
diff --git a/modules/audio_processing/audio_processing_impl.h b/modules/audio_processing/audio_processing_impl.h
index bf1d22e..22cdadd 100644
--- a/modules/audio_processing/audio_processing_impl.h
+++ b/modules/audio_processing/audio_processing_impl.h
@@ -21,6 +21,7 @@
 #include "api/function_view.h"
 #include "modules/audio_processing/aec3/echo_canceller3.h"
 #include "modules/audio_processing/agc/agc_manager_direct.h"
+#include "modules/audio_processing/agc/analog_gain_stats_reporter.h"
 #include "modules/audio_processing/agc/gain_control.h"
 #include "modules/audio_processing/audio_buffer.h"
 #include "modules/audio_processing/capture_levels_adjuster/capture_levels_adjuster.h"
@@ -531,6 +532,9 @@
   RmsLevel capture_output_rms_ RTC_GUARDED_BY(mutex_capture_);
   int capture_rms_interval_counter_ RTC_GUARDED_BY(mutex_capture_) = 0;
 
+  AnalogGainStatsReporter analog_gain_stats_reporter_
+      RTC_GUARDED_BY(mutex_capture_);
+
   // Lock protection not needed.
   std::unique_ptr<
       SwapQueue<std::vector<int16_t>, RenderQueueItemVerifier<int16_t>>>