Surface the IntelligibilityEnhancer on MediaConstraints

webrtc/media/engine/webrtcvoiceengine.h

Index: webrtc/media/engine/webrtcvoiceengine.h
diff --git a/webrtc/media/engine/webrtcvoiceengine.h b/webrtc/media/engine/webrtcvoiceengine.h
index 1cc550430435b4dedadd20144c0ce0c109119be0..29f9eed54c4dc7aa422733dd8f00c4d77743c5f8 100644
--- a/webrtc/media/engine/webrtcvoiceengine.h
+++ b/webrtc/media/engine/webrtcvoiceengine.h
@@ -120,13 +120,14 @@ class WebRtcVoiceEngine final : public webrtc::TraceCallback  {
   bool is_dumping_aec_ = false;
 
   webrtc::AgcConfig default_agc_config_;
-  // Cache received extended_filter_aec, delay_agnostic_aec and experimental_ns
-  // values, and apply them in case they are missing in the audio options. We
-  // need to do this because SetExtraOptions() will revert to defaults for
-  // options which are not provided.
+  // Cache received extended_filter_aec, delay_agnostic_aec, experimental_ns and
+  // intelligibility_enhancer values, and apply them in case they are missing
+  // in the audio options. We need to do this because SetExtraOptions() will
+  // revert to defaults for options which are not provided.
   rtc::Optional<bool> extended_filter_aec_;
   rtc::Optional<bool> delay_agnostic_aec_;
   rtc::Optional<bool> experimental_ns_;
+  rtc::Optional<bool> intelligibility_enhancer_;
 
   RTC_DISALLOW_IMPLICIT_CONSTRUCTORS(WebRtcVoiceEngine);
 };