Field trial support to whenever possible turn off the AGC and HPF

webrtc/media/engine/webrtcvoiceengine.cc

Index: webrtc/media/engine/webrtcvoiceengine.cc
diff --git a/webrtc/media/engine/webrtcvoiceengine.cc b/webrtc/media/engine/webrtcvoiceengine.cc
index 2b0f72aef1ff5ee8786f5a73e0a0e58d4f29147b..210313896004d2efd39484b2aaa52a43138b94d1 100644
--- a/webrtc/media/engine/webrtcvoiceengine.cc
+++ b/webrtc/media/engine/webrtcvoiceengine.cc
@@ -336,6 +336,7 @@ bool WebRtcVoiceEngine::ApplyOptions(const AudioOptions& options_in) {
   LOG(LS_INFO) << "WebRtcVoiceEngine::ApplyOptions: " << options_in.ToString();
   AudioOptions options = options_in;  // The options are modified below.
 
+  // Set and adjust echo canceller options.
   // kEcConference is AEC with high suppression.
   webrtc::EcModes ec_mode = webrtc::kEcConference;
   if (options.aecm_generate_comfort_noise) {
@@ -345,21 +346,13 @@ bool WebRtcVoiceEngine::ApplyOptions(const AudioOptions& options_in) {
   }
 
 #if defined(WEBRTC_IOS)
-  // On iOS, VPIO provides built-in EC, NS and AGC.
+  // On iOS, VPIO provides built-in EC.
   options.echo_cancellation = rtc::Optional<bool>(false);
-  options.auto_gain_control = rtc::Optional<bool>(false);
-  options.noise_suppression = rtc::Optional<bool>(false);
-  LOG(LS_INFO)
-      << "Always disable AEC, NS and AGC on iOS. Use built-in instead.";
+  options.extended_filter_aec = rtc::Optional<bool>(false);
+  LOG(LS_INFO) << "Always disable AEC on iOS. Use built-in instead.";
 #elif defined(ANDROID)
   ec_mode = webrtc::kEcAecm;
-#endif
-
-#if defined(WEBRTC_IOS) || defined(ANDROID)
-  options.typing_detection = rtc::Optional<bool>(false);
-  options.experimental_agc = rtc::Optional<bool>(false);
   options.extended_filter_aec = rtc::Optional<bool>(false);
-  options.experimental_ns = rtc::Optional<bool>(false);
 #endif
 
   // Delay Agnostic AEC automatically turns on EC if not set except on iOS
@@ -376,6 +369,43 @@ bool WebRtcVoiceEngine::ApplyOptions(const AudioOptions& options_in) {
   }
 #endif
 
+// Set and adjust noise suppressor options.
+#if defined(WEBRTC_IOS)
+  // On iOS, VPIO provides built-in NS.
+  options.noise_suppression = rtc::Optional<bool>(false);
+  options.typing_detection = rtc::Optional<bool>(false);
+  options.experimental_ns = rtc::Optional<bool>(false);
+  LOG(LS_INFO) << "Always disable NS on iOS. Use built-in instead.";
+#elif defined(ANDROID)
+  options.typing_detection = rtc::Optional<bool>(false);
+  options.experimental_ns = rtc::Optional<bool>(false);
+#endif
+
+// Set and adjust gain control options.
+#if defined(WEBRTC_IOS)
+  // On iOS, VPIO provides built-in AGC.
+  options.auto_gain_control = rtc::Optional<bool>(false);
+  options.experimental_agc = rtc::Optional<bool>(false);
+  LOG(LS_INFO) << "Always disable AGC on iOS. Use built-in instead.";
+#elif defined(ANDROID)
+  options.experimental_agc = rtc::Optional<bool>(false);
+#endif
+
+#if defined(WEBRTC_IOS) || defined(WEBRTC_ANDROID)
+  // Turn off the gain control if specified by the field trial. The purpose of the field trial is to reduce the amount of resampling performed inside the audio processing module on mobile platforms by whenever possible turning off the fixed AGC mode and the high-pass filter. (https://bugs.chromium.org/p/webrtc/issues/detail?id=6181).
+  if (webrtc::field_trial::IsEnabled(
+          "WebRTC-Audio-MinimizeResamplingOnMobile")) {
+    options.auto_gain_control = rtc::Optional<bool>(false);
+    LOG(LS_INFO) << "Disable AGC according to field trial.";
+    if (!(options.noise_suppression.value_or(false) or
+          options.echo_cancellation.value_or(false))) {
+      // If possible, turn off the high-pass filter.
+      LOG(LS_INFO) << "Disable high-pass filter in response to field trial.";
+      options.highpass_filter = rtc::Optional<bool>(false);
+    }
+  }
+#endif
+
 #if (WEBRTC_INTELLIGIBILITY_ENHANCER == 0)
   // Hardcode the intelligibility enhancer to be off.
   options.intelligibility_enhancer = rtc::Optional<bool>(false);