Simplify registration of RTP-header extensions.

webrtc/modules/rtp_rtcp/include/rtp_rtcp.h

Index: webrtc/modules/rtp_rtcp/include/rtp_rtcp.h
diff --git a/webrtc/modules/rtp_rtcp/include/rtp_rtcp.h b/webrtc/modules/rtp_rtcp/include/rtp_rtcp.h
index e0ace4c775d76c9df39d0d9a69954cb9c8b50df2..a47d3fefae57212e7109b9499493ed820026f633 100644
--- a/webrtc/modules/rtp_rtcp/include/rtp_rtcp.h
+++ b/webrtc/modules/rtp_rtcp/include/rtp_rtcp.h
@@ -12,6 +12,7 @@
 #define WEBRTC_MODULES_RTP_RTCP_INCLUDE_RTP_RTCP_H_
 
 #include <set>
+#include <string>
 #include <utility>
 #include <vector>
 
@@ -26,6 +27,8 @@ class RtpReceiver;
 class Transport;
 class RtcEventLog;
 
+RTPExtensionType StringToRtpExtensionType(const std::string& extension);
+
 namespace rtcp {
 class TransportFeedback;
 }