Add a new UMA metric in APM to track incoming capture-side audio level

webrtc/modules/audio_processing/audio_processing_impl.h

Index: webrtc/modules/audio_processing/audio_processing_impl.h
diff --git a/webrtc/modules/audio_processing/audio_processing_impl.h b/webrtc/modules/audio_processing/audio_processing_impl.h
index d171715a96412642e98df7dc68bef60d4105f621..f88abe3bb609ca903b2766df9c0bb355af1af73f 100644
--- a/webrtc/modules/audio_processing/audio_processing_impl.h
+++ b/webrtc/modules/audio_processing/audio_processing_impl.h
@@ -25,6 +25,7 @@
 #include "webrtc/modules/audio_processing/audio_buffer.h"
 #include "webrtc/modules/audio_processing/include/audio_processing.h"
 #include "webrtc/modules/audio_processing/render_queue_item_verifier.h"
+#include "webrtc/modules/audio_processing/rms_level.h"
 #include "webrtc/system_wrappers/include/file_wrapper.h"
 
 #ifdef WEBRTC_AUDIOPROC_DEBUG_DUMP
@@ -406,6 +407,9 @@ class AudioProcessingImpl : public AudioProcessing {
   std::vector<float> red_render_queue_buffer_ GUARDED_BY(crit_render_);
   std::vector<float> red_capture_queue_buffer_ GUARDED_BY(crit_capture_);
 
+  RMSLevel rms_ GUARDED_BY(crit_capture_);
+  int rms_interval_counter_ GUARDED_BY(crit_capture_) = 0;
+
   // Lock protection not needed.
   std::unique_ptr<SwapQueue<std::vector<float>, RenderQueueItemVerifier<float>>>
       aec_render_signal_queue_;