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

Index: webrtc/modules/audio_processing/level_controller/level_controller.h
diff --git a/webrtc/modules/audio_processing/level_controller/level_controller.h b/webrtc/modules/audio_processing/level_controller/level_controller.h
index 1d8e043cce410adbb1b07e970b41bf75f08a4395..05784beeb457c9492123416573e44bcd47730444 100644
--- a/webrtc/modules/audio_processing/level_controller/level_controller.h
+++ b/webrtc/modules/audio_processing/level_controller/level_controller.h
@@ -38,11 +38,18 @@ class LevelController {
   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 {
@@ -80,6 +87,7 @@ class LevelController {
   float dc_level_[2];
   float dc_forgetting_factor_;
   float last_gain_;
+  bool gain_jumpstart_ = false;
 
   RTC_DISALLOW_COPY_AND_ASSIGN(LevelController);
 };