Add support for negotiating RTCP with reduced size.

talk/media/base/mediachannel.h

Index: talk/media/base/mediachannel.h
diff --git a/talk/media/base/mediachannel.h b/talk/media/base/mediachannel.h
index ed4142969b96e74934b1416d760c3aa08b05e4af..9548df2749ba8bd0073ea71e53a35b37d6ddb370 100644
--- a/talk/media/base/mediachannel.h
+++ b/talk/media/base/mediachannel.h
@@ -1009,6 +1009,10 @@ struct DataMediaInfo {
   std::vector<DataReceiverInfo> receivers;
 };
 
+struct RtcpParameters {
+  bool reduced_size = false;
+};
+
 template <class Codec>
 struct RtpParameters {
   virtual std::string ToString() {
@@ -1023,6 +1027,7 @@ struct RtpParameters {
   std::vector<Codec> codecs;
   std::vector<RtpHeaderExtension> extensions;
   // TODO(pthatcher): Add streams.
+  RtcpParameters rtcp;
 };
 
 template <class Codec, class Options>