iOS: Add trendline filter to field trials.

webrtc/sdk/objc/Framework/Classes/RTCFieldTrials.mm

Index: webrtc/sdk/objc/Framework/Classes/RTCFieldTrials.mm
diff --git a/webrtc/sdk/objc/Framework/Classes/RTCFieldTrials.mm b/webrtc/sdk/objc/Framework/Classes/RTCFieldTrials.mm
index 3057a17aedf34fdf089ffc66198b802a2338e335..224f7fd5956a1cae8a911846aaa4a2567d64c5c9 100644
--- a/webrtc/sdk/objc/Framework/Classes/RTCFieldTrials.mm
+++ b/webrtc/sdk/objc/Framework/Classes/RTCFieldTrials.mm
@@ -16,24 +16,31 @@
 
 #include "webrtc/system_wrappers/include/field_trial_default.h"
 
-static NSString * const kRTCEnableImprovedBitrateEstimateString =
-    @"WebRTC-ImprovedBitrateEstimate/Enabled/";
-static NSString * const kRTCEnableAudioSendSideBweString =
-    @"WebRTC-Audio-SendSideBwe/Enabled/";
-static NSString * const kRTCEnableFlexFec03String =
-    @"WebRTC-FlexFEC-03/Enabled/";
+NSString * const kRTCFieldTrialAudioSendSideBweKey = @"WebRTC-Audio-SendSideBwe";
+NSString * const kRTCFieldTrialFlexFec03Key = @"WebRTC-FlexFEC-03";
+NSString * const kRTCFieldTrialImprovedBitrateEstimateKey = @"WebRTC-ImprovedBitrateEstimate";
+NSString * const kRTCFieldTrialTrendlineFilterKey = @"WebRTC-BweTrendlineFilter";
+NSString * const kRTCFieldTrialEnabledValue = @"Enabled";
+
 static std::unique_ptr<char[]> gFieldTrialInitString;
 
-void RTCInitFieldTrials(RTCFieldTrialOptions options) {
-  NSMutableString *fieldTrialInitString = [NSMutableString string];
-  if (options & RTCFieldTrialOptionsImprovedBitrateEstimate) {
-    [fieldTrialInitString appendString:kRTCEnableImprovedBitrateEstimateString];
-  }
-  if (options & RTCFieldTrialOptionsAudioSendSideBwe) {
-    [fieldTrialInitString appendString:kRTCEnableAudioSendSideBweString];
+NSString *RTCFieldTrialTrendlineFilterValue(
+    size_t windowSize, double smoothingCoeff, double thresholdGain) {
+  NSString *format = @"Enabled-%zu,%lf,%lf";
+  return [NSString stringWithFormat:format, windowSize, smoothingCoeff, thresholdGain];
+}
+
+void RTCInitFieldTrialDictionary(NSDictionary<NSString *, NSString *> *fieldTrials) {
+  if (!fieldTrials) {
+    RTCLogWarning(@"No fieldTrials provided.");
+    return;
   }
-  if (options & RTCFieldTrialOptionsFlexFec03) {
-    [fieldTrialInitString appendString:kRTCEnableFlexFec03String];
+  // Assemble the keys and values into the field trial string.
+  // We don't perform any extra format checking. That should be done by the underlying WebRTC calls.
+  NSMutableString *fieldTrialInitString = [NSMutableString string];
+  for (NSString *key in fieldTrials) {
+    NSString *fieldTrialEntry = [NSString stringWithFormat:@"%@/%@/", key, fieldTrials[key]];
+    [fieldTrialInitString appendString:fieldTrialEntry];
   }
   size_t len = fieldTrialInitString.length + 1;
   gFieldTrialInitString.reset(new char[len]);