Reland of added functionality for specifying the initial signal level to use for the gain estimation

webrtc/modules/audio_processing/include/audio_processing.h

Index: webrtc/modules/audio_processing/include/audio_processing.h
diff --git a/webrtc/modules/audio_processing/include/audio_processing.h b/webrtc/modules/audio_processing/include/audio_processing.h
index 172da0891f3bcd362b4796b23a3b4b59b0b9a6f7..3848d0bc760c84d303e14d6591eeacb5a1568768 100644
--- a/webrtc/modules/audio_processing/include/audio_processing.h
+++ b/webrtc/modules/audio_processing/include/audio_processing.h
@@ -20,6 +20,7 @@
 #include <vector>
 
 #include "webrtc/base/arraysize.h"
+#include "webrtc/base/optional.h"
 #include "webrtc/base/platform_file.h"
 #include "webrtc/modules/audio_processing/beamformer/array_util.h"
 #include "webrtc/modules/audio_processing/include/config.h"
@@ -251,7 +252,14 @@ class AudioProcessing {
   // The config is applied by passing the struct to the ApplyConfig method.
   struct Config {
     struct LevelController {
+      LevelController();
+      ~LevelController();
       bool enabled = false;
+
+      // Sets the initial peak level to use inside the level controller in order
+      // to compute the signal gain. The unit for the peak level is dBFS and
+      // the allowed range is [-100, 0].
+      rtc::Optional<float> initial_level;
     } level_controller;
   };