Cast: Add capabity to parse receiver and sender log messages over RTCP.

media/cast/logging/logging_defines.cc

Index: media/cast/logging/logging_defines.cc
diff --git a/media/cast/logging/logging_defines.cc b/media/cast/logging/logging_defines.cc
index d70fc63efd8271cbc2718df37c3834f20c21da1a..85abe7c5d45dbb1c5080e39d3533072bb4eab4f8 100644
--- a/media/cast/logging/logging_defines.cc
+++ b/media/cast/logging/logging_defines.cc
@@ -23,6 +23,10 @@ CastLoggingConfig GetDefaultCastLoggingConfig() {
 
 std::string CastLoggingToString(CastLoggingEvent event) {
   switch (event) {
+    case(kUnknown):
+      // Can happen if the sender and receiver of RTCP log messages are not
+      // aligned.
+      return "Unknown";
     case(kRttMs):
       return "RttMs";
     case(kPacketLoss):