Replace MediaContentDirection with RtpTransceiverDirection

Bug: webrtc:8558
Change-Id: I410d17cce235e0b42038cf0b125fd916010f50ae
Reviewed-on: https://webrtc-review.googlesource.com/24745
Commit-Queue: Steve Anton <steveanton@webrtc.org>
Reviewed-by: Peter Thatcher <pthatcher@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#20922}

pc/rtpmediautils.cc

@@ -50,4 +50,19 @@ RtpTransceiverDirection RtpTransceiverDirectionReversed(
   return direction;
 }
 
+const char* RtpTransceiverDirectionToString(RtpTransceiverDirection direction) {
+  switch (direction) {
+    case RtpTransceiverDirection::kSendRecv:
+      return "kSendRecv";
+    case RtpTransceiverDirection::kSendOnly:
+      return "kSendOnly";
+    case RtpTransceiverDirection::kRecvOnly:
+      return "kRecvOnly";
+    case RtpTransceiverDirection::kInactive:
+      return "kInactive";
+  }
+  RTC_NOTREACHED();
+  return "";
+}
+
 }  // namespace webrtc