Use low cut filtering whenever NS or AEC are enabled

These submodules implicitly rely on low cut filtering being enabled.

This CL clarifies a distinction:
High pass filtering is a feature that users can enable, according to the WebRTC standard.
Low cut filtering is a processing effect that is applied when any of the following is active:
- high pass filter
- noise suppression
- builtin echo cancellation

Bug: webrtc:9535
Change-Id: I9474276fb11354ea3b01e65a0699f6c29263770b
Reviewed-on: https://webrtc-review.googlesource.com/102600
Reviewed-by: Per Åhgren <peah@webrtc.org>
Commit-Queue: Sam Zackrisson <saza@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#24892}

modules/audio_processing/audio_processing_impl.h

@@ -178,7 +178,7 @@ class AudioProcessingImpl : public AudioProcessing {
                        bool render_pre_processor_enabled,
                        bool capture_analyzer_enabled);
     // Updates the submodule state and returns true if it has changed.
-    bool Update(bool low_cut_filter_enabled,
+    bool Update(bool high_pass_filter_enabled,
                 bool echo_canceller_enabled,
                 bool mobile_echo_controller_enabled,
                 bool residual_echo_detector_enabled,
@@ -197,12 +197,13 @@ class AudioProcessingImpl : public AudioProcessing {
     bool RenderMultiBandSubModulesActive() const;
     bool RenderFullBandProcessingActive() const;
     bool RenderMultiBandProcessingActive() const;
+    bool LowCutFilteringRequired() const;
 
    private:
     const bool capture_post_processor_enabled_ = false;
     const bool render_pre_processor_enabled_ = false;
     const bool capture_analyzer_enabled_ = false;
-    bool low_cut_filter_enabled_ = false;
+    bool high_pass_filter_enabled_ = false;
     bool echo_canceller_enabled_ = false;
     bool mobile_echo_controller_enabled_ = false;
     bool residual_echo_detector_enabled_ = false;