Report SRTP error codes to UMA

Bug: webrtc:8996
Change-Id: I75de77ed15c2829425c00f57ebd07109803425db
Reviewed-on: https://webrtc-review.googlesource.com/63122
Reviewed-by: Zhi Huang <zhihuang@webrtc.org>
Reviewed-by: Taylor Brandstetter <deadbeef@webrtc.org>
Commit-Queue: Steve Anton <steveanton@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22521}

api/umametrics.h

@@ -42,6 +42,9 @@ enum PeerConnectionEnumCounterType {
   kEnumCounterSdpSemanticNegotiated,
   kEnumCounterKeyProtocolMediaType,
   kEnumCounterSdpFormatReceived,
+  // The next 2 counters log the value of srtp_err_status_t defined in libsrtp.
+  kEnumCounterSrtpUnprotectError,
+  kEnumCounterSrtcpUnprotectError,
   kPeerConnectionEnumCounterMax
 };