Optionally disable digital gain control in ExperimentalAgc.

This CL adds a flag to optionally disable the digital gain control in
ExperimentalAgc. With the flag, Experimental Agc (henceforth AGC1)
only controls the adaptive analog gain. This flag can be combined to
that which activates AGC2. That way, one can enable the hybrid AGC
configuration AGC1 analog only + AGC2 fixed+adaptive digital.

Previously, there was a flag "use_agc2_digital_adaptive" in
AgcManagerDirect. Our ambition was that to activate the hybrid mode
described above with this flag. The behavior of the flag was not
implemented.

To activate the hybrid mode after this CL, set
ExperimentalAgc::digital_adaptive_disabled=true and
AudioProcessing::Config::GainController2::enabled=true.

We also add flags for these settings in audioproc_f.
Then the required settings are currently

  audioproc_f --agc2 1 --agc 1 --experimental_agc 1 \
      --experimental_agc_disable_digital_adaptive 1 \
      -i [INPUT]

Bug: webrtc:7494
Change-Id: Iea798dc3899cec83d30ba71caba787262fcaef41
Reviewed-on: https://webrtc-review.googlesource.com/89740
Commit-Queue: Alex Loiko <aleloi@webrtc.org>
Reviewed-by: Alessio Bazzica <alessiob@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24249}
diff --git a/modules/audio_processing/include/audio_processing.h b/modules/audio_processing/include/audio_processing.h
index 291e531..41b45aa 100644
--- a/modules/audio_processing/include/audio_processing.h
+++ b/modules/audio_processing/include/audio_processing.h
@@ -121,10 +121,10 @@
   explicit ExperimentalAgc(bool enabled) : enabled(enabled) {}
   ExperimentalAgc(bool enabled,
                   bool enabled_agc2_level_estimator,
-                  bool enabled_agc2_digital_adaptive)
+                  bool digital_adaptive_disabled)
       : enabled(enabled),
         enabled_agc2_level_estimator(enabled_agc2_level_estimator),
-        enabled_agc2_digital_adaptive(enabled_agc2_digital_adaptive) {}
+        digital_adaptive_disabled(digital_adaptive_disabled) {}
 
   ExperimentalAgc(bool enabled, int startup_min_volume)
       : enabled(enabled), startup_min_volume(startup_min_volume) {}
@@ -138,7 +138,7 @@
   // Lowest microphone level that will be applied in response to clipping.
   int clipped_level_min = kClippedLevelMin;
   bool enabled_agc2_level_estimator = false;
-  bool enabled_agc2_digital_adaptive = false;
+  bool digital_adaptive_disabled = false;
 };
 
 // Use to enable experimental noise suppression. It can be set in the