Introduced the new parameter setting scheme for activating the high-pass filter in APM

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 aec4ed7086d992b3bcb01d154a5d49f1dc392406..b941398a45d61ae4818e47d24b7e8adab2eb28da 100644
--- a/webrtc/modules/audio_processing/audio_processing_impl.h
+++ b/webrtc/modules/audio_processing/audio_processing_impl.h
@@ -17,6 +17,7 @@
 #include <vector>
 
 #include "webrtc/base/criticalsection.h"
+#include "webrtc/base/function_view.h"
 #include "webrtc/base/gtest_prod_util.h"
 #include "webrtc/base/ignore_wundef.h"
 #include "webrtc/base/swap_queue.h"
@@ -124,11 +125,16 @@ class AudioProcessingImpl : public AudioProcessing {
   EchoCancellation* echo_cancellation() const override;
   EchoControlMobile* echo_control_mobile() const override;
   GainControl* gain_control() const override;
+  // TODO(peah): Deprecate this API call.
   HighPassFilter* high_pass_filter() const override;
   LevelEstimator* level_estimator() const override;
   NoiseSuppression* noise_suppression() const override;
   VoiceDetection* voice_detection() const override;
 
+  // TODO(peah): Remove these two methods once the new API allows that.
+  void MutateConfig(std::function<void(AudioProcessing::Config*)> mutator);
+  AudioProcessing::Config GetConfig() const;
+
  protected:
   // Overridden in a mock.
   virtual int InitializeLocked()
@@ -143,11 +149,14 @@ class AudioProcessingImpl : public AudioProcessing {
   struct ApmPublicSubmodules;
   struct ApmPrivateSubmodules;
 
+  // Submodule interface implementations.
+  std::unique_ptr<HighPassFilter> high_pass_filter_impl_;
+
   class ApmSubmoduleStates {
    public:
     ApmSubmoduleStates();
     // Updates the submodule state and returns true if it has changed.
-    bool Update(bool high_pass_filter_enabled,
+    bool Update(bool low_cut_filter_enabled,

[the sun, 2016/10/28 12:38:32]

I'm not so sure about this use of low cut vs high pass - it is a bit confusing.
Maybe it is better to just stick to one name, or use LowCutFilter only at the
very lowest level, where the filter is actually being owned and instantiated.

[peah-webrtc, 2016/10/28 12:47:46]

I agree that it is confusing. But I think using the name high_pass_filter in
general is deceivingly simple for now and 

I view it as this
-High pass filtering is an effect that is provided by the APM.
-The high pass filtering effect is achieved using the low cut filter
functionality.
-The low cut filter functionality is in some scenarios needed/needs to be
activated even though the high pass filtering effect is turned off (that is what
upcoming CLs will change this to be).

Therefore I think it makes sens to differ between the effect provided by the APM
and the functionality we use to achieve the effect.

In this case, the the low_cut_filter_enabled flag is used in the
ApmSubmoduleStates class to determine when conditional reinitialization is
needed. For that, it makes much more sense to use the term low cut filter rather
than the high pass filter, as it is not the activation of the high pass
filtering effect but rather the activation of the low cut processing
functionality that possibly triggers the conditional reinitialization.

I did the partitioning so that everything that is publicly visible outside APM
still uses the high pass filter term. The log lines is one such example.

                 bool echo_canceller_enabled,
                 bool mobile_echo_controller_enabled,
                 bool noise_suppressor_enabled,
@@ -164,7 +173,7 @@ class AudioProcessingImpl : public AudioProcessing {
     bool RenderMultiBandProcessingActive() const;
 
    private:
-    bool high_pass_filter_enabled_ = false;
+    bool low_cut_filter_enabled_ = false;
     bool echo_canceller_enabled_ = false;
     bool mobile_echo_controller_enabled_ = false;
     bool noise_suppressor_enabled_ = false;
@@ -234,6 +243,7 @@ class AudioProcessingImpl : public AudioProcessing {
   int InitializeLocked(const ProcessingConfig& config)
       EXCLUSIVE_LOCKS_REQUIRED(crit_render_, crit_capture_);
   void InitializeLevelController() EXCLUSIVE_LOCKS_REQUIRED(crit_capture_);
+  void InitializeLowCutFilter() EXCLUSIVE_LOCKS_REQUIRED(crit_capture_);
 
   void EmptyQueuedRenderAudio();
   void AllocateRenderQueue()