Add media constraint-key constants for generating offers and answers

webrtc/sdk/objc/Framework/Classes/PeerConnection/RTCMediaConstraints.mm

Index: webrtc/sdk/objc/Framework/Classes/PeerConnection/RTCMediaConstraints.mm
diff --git a/webrtc/sdk/objc/Framework/Classes/PeerConnection/RTCMediaConstraints.mm b/webrtc/sdk/objc/Framework/Classes/PeerConnection/RTCMediaConstraints.mm
index 3b9d84584113bd458d139810309eb925eda037f6..c686b5643c3ae3f20f83c9f7ae279208e33e95b8 100644
--- a/webrtc/sdk/objc/Framework/Classes/PeerConnection/RTCMediaConstraints.mm
+++ b/webrtc/sdk/objc/Framework/Classes/PeerConnection/RTCMediaConstraints.mm
@@ -35,6 +35,15 @@ NSString * const kRTCMediaConstraintsLevelControl =
 NSString * const kRTCMediaConstraintsAudioNetworkAdaptorConfig =
     @(webrtc::MediaConstraintsInterface::kAudioNetworkAdaptorConfig);
 
+NSString * const kRTCMediaConstraintsIceRestart =
+    @(webrtc::MediaConstraintsInterface::kIceRestart);
+NSString * const kRTCMediaConstraintsOfferToReceiveAudio =
+    @(webrtc::MediaConstraintsInterface::kOfferToReceiveAudio);
+NSString * const kRTCMediaConstraintsOfferToReceiveVideo =
+    @(webrtc::MediaConstraintsInterface::kOfferToReceiveVideo);
+NSString * const kRTCMediaConstraintsVoiceActivityDetection =
+    @(webrtc::MediaConstraintsInterface::kVoiceActivityDetection);
+
 NSString * const kRTCMediaConstraintsValueTrue =
     @(webrtc::MediaConstraintsInterface::kValueTrue);
 NSString * const kRTCMediaConstraintsValueFalse =