Add RtpHeaderExtension to avoid client breakage

webrtc/pc/mediasession.h

Index: webrtc/pc/mediasession.h
diff --git a/webrtc/pc/mediasession.h b/webrtc/pc/mediasession.h
index 0a04bcf93f575587d2a82184400e574be41c9e80..272775e6b501c4af9f38251f5670d50f3a396a99 100644
--- a/webrtc/pc/mediasession.h
+++ b/webrtc/pc/mediasession.h
@@ -209,6 +209,13 @@ class MediaContentDescription : public ContentDescription {
     rtp_header_extensions_.push_back(ext);
     rtp_header_extensions_set_ = true;
   }
+  void AddRtpHeaderExtension(const cricket::RtpHeaderExtension& ext) {
+    webrtc::RtpExtension webrtc_extension;
+    webrtc_extension.uri = ext.uri;
+    webrtc_extension.id = ext.id;
+    rtp_header_extensions_.push_back(webrtc_extension);
+    rtp_header_extensions_set_ = true;
+  }
   void ClearRtpHeaderExtensions() {
     rtp_header_extensions_.clear();
     rtp_header_extensions_set_ = true;