iOS: Add trendline filter to field trials.

webrtc/sdk/objc/Framework/Headers/WebRTC/RTCFieldTrials.h

Index: webrtc/sdk/objc/Framework/Headers/WebRTC/RTCFieldTrials.h
diff --git a/webrtc/sdk/objc/Framework/Headers/WebRTC/RTCFieldTrials.h b/webrtc/sdk/objc/Framework/Headers/WebRTC/RTCFieldTrials.h
index 504ff7a885357bc457c59a58ca348a5cca1b0118..ee997888c1e020a694f78d8655504da1986dbb2e 100644
--- a/webrtc/sdk/objc/Framework/Headers/WebRTC/RTCFieldTrials.h
+++ b/webrtc/sdk/objc/Framework/Headers/WebRTC/RTCFieldTrials.h
@@ -12,14 +12,23 @@
 
 #import <WebRTC/RTCMacros.h>
 
-typedef NS_OPTIONS(NSUInteger, RTCFieldTrialOptions) {
-  RTCFieldTrialOptionsNone = 0,
-  RTCFieldTrialOptionsImprovedBitrateEstimate = 1 << 0,
-  RTCFieldTrialOptionsAudioSendSideBwe = 1 << 1,
-  RTCFieldTrialOptionsFlexFec03 = 1 << 2,
-};
+/** The only valid value for the following if set is kRTCFieldTrialEnabledValue. */
+RTC_EXTERN NSString * const kRTCFieldTrialAudioSendSideBweKey;
+RTC_EXTERN NSString * const kRTCFieldTrialFlexFec03Key;
+RTC_EXTERN NSString * const kRTCFieldTrialImprovedBitrateEstimateKey;
 
-/** Must be called before any other call into WebRTC. See:
+/** The valid value for field trials above. */
+RTC_EXTERN NSString * const kRTCFieldTrialEnabledValue;
+
+/** Use a string returned by RTCFieldTrialTrendlineFilterValue as the value. */
+RTC_EXTERN NSString * const kRTCFieldTrialTrendlineFilterKey;
+/** Returns a valid value for kRTCFieldTrialTrendlineFilterKey. */
+RTC_EXTERN NSString *RTCFieldTrialTrendlineFilterValue(
+    size_t windowSize, double smoothingCoeff, double thresholdGain);
+
+/** Initialize field trials using a dictionary mapping field trial keys to their values. See above
+ *  for valid keys and values.
+ *  Must be called before any other call into WebRTC. See:
  *  webrtc/system_wrappers/include/field_trial_default.h
  */
-RTC_EXTERN void RTCInitFieldTrials(RTCFieldTrialOptions options);
+RTC_EXTERN void RTCInitFieldTrialDictionary(NSDictionary<NSString *, NSString *> *fieldTrials);