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

webrtc/modules/audio_processing/level_controller/level_controller.h

 /*
  *  Copyright (c) 2016 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 20 matching lines @@
 
 class LevelController {
  public:
   LevelController();
   ~LevelController();
 
   void Initialize(int sample_rate_hz);
   void Process(AudioBuffer* audio);
   float GetLastGain() { return last_gain_; }
 
+  // TODO(peah): This method is a temporary solution used to take control
+  // over the parameters in the audio processing module and is likely to change.

[the sun, 2016/09/14 10:00:59]

I don't understand this comment. How do we take control over the APMs
parameters? We only see the LCs parameters? We just apply those, like the name
says, latch them in, if you're EE.

Would be better to explain why it is a temporary solution; it should be done in
ctor instead.

[peah-webrtc, 2016/09/16 07:11:07]

Totally agree. 

Done.

+  void ApplyConfig(const AudioProcessing::Config::LevelController& config);
   // Validates a config.
   static bool Validate(const AudioProcessing::Config::LevelController& config);
   // Dumps a config to a string.
   static std::string ToString(
       const AudioProcessing::Config::LevelController& config);
+  // 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].
+  void SetInitialLevel(float level);

[the sun, 2016/09/14 10:00:59]

Where is this used? The idea of setting up from a Config struct is to avoid
individual setters.

[peah-webrtc, 2016/09/16 07:11:07]

This is a leftover from the former CL. Sorry about that! Removed it.

Done.

 
  private:
   class Metrics {
    public:
     Metrics() { Initialize(AudioProcessing::kSampleRate48kHz); }
     void Initialize(int sample_rate_hz);
     void Update(float long_term_peak_level,
                 float noise_level,
                 float gain,
                 float frame_peak_level);
@@ skipping 17 matching lines @@
   SignalClassifier signal_classifier_;
   NoiseLevelEstimator noise_level_estimator_;
   PeakLevelEstimator peak_level_estimator_;
   SaturatingGainEstimator saturating_gain_estimator_;
   Metrics metrics_;
   rtc::Optional<int> sample_rate_hz_;
   static int instance_count_;
   float dc_level_[2];
   float dc_forgetting_factor_;
   float last_gain_;
+  bool gain_jumpstart_ = false;
 
   RTC_DISALLOW_COPY_AND_ASSIGN(LevelController);
 };
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_MODULES_AUDIO_PROCESSING_LEVEL_CONTROLLER_LEVEL_CONTROLLER_H_