Add new variance update option and unittests for intelligibility

webrtc/modules/audio_processing/intelligibility/intelligibility_enhancer.h

Index: webrtc/modules/audio_processing/intelligibility/intelligibility_enhancer.h
diff --git a/webrtc/modules/audio_processing/intelligibility/intelligibility_enhancer.h b/webrtc/modules/audio_processing/intelligibility/intelligibility_enhancer.h
index 8125707f120981c40817152a80bcbea43f2e3006..ee59584e3e412c83109f6cf97f88a5f20352f678 100644
--- a/webrtc/modules/audio_processing/intelligibility/intelligibility_enhancer.h
+++ b/webrtc/modules/audio_processing/intelligibility/intelligibility_enhancer.h
@@ -83,6 +83,8 @@ class IntelligibilityEnhancer {
     AudioSource source_;
   };
   friend class TransformCallback;
+  FRIEND_TEST_ALL_PREFIXES(IntelligibilityEnhancerTest, TestErbCreation);
+  FRIEND_TEST_ALL_PREFIXES(IntelligibilityEnhancerTest, TestSolveForGains);
 
   // Sends streams to ProcessClearBlock or ProcessNoiseBlock based on source.
   void DispatchAudio(AudioSource source,
@@ -97,6 +99,12 @@ class IntelligibilityEnhancer {
   // Computes and sets modified gains.
   void AnalyzeClearBlock(float power_target);
 
+  // Bisection search for optimal |lambda|.
+  void SolveForLambda(float power_target, float power_bot, float power_top);
+
+  // Transforms freq gains to ERB gains.
+  void UpdateErbGains();
+
   // Updates variance calculation for noise input with |in_block|.
   void ProcessNoiseBlock(const std::complex<float>* in_block,
                          std::complex<float>* out_block);
@@ -127,6 +135,8 @@ class IntelligibilityEnhancer {
   static const float kConfigRho;  // Default production and interpretation SNR.
   static const float kKbdAlpha;
   static const float kGainChangeLimit;
+  static const float kLambdaBot;  // Extreme values in bisection
+  static const float kLambdaTop;  // search for lambda.
 
   const int freqs_;         // Num frequencies in frequency domain.
   const int window_size_;   // Window size in samples; also the block size.