[Cast Channel] Add support for nonce challenge to Cast channel authentication.

extensions/browser/api/cast_channel/cast_message_util.cc

Index: extensions/browser/api/cast_channel/cast_message_util.cc
diff --git a/extensions/browser/api/cast_channel/cast_message_util.cc b/extensions/browser/api/cast_channel/cast_message_util.cc
index 3726efdacbc819bca9c414530e97e94b72239875..adb4f0f048d8cbb35165e99892a8637e04bff95d 100644
--- a/extensions/browser/api/cast_channel/cast_message_util.cc
+++ b/extensions/browser/api/cast_channel/cast_message_util.cc
@@ -138,10 +138,10 @@ std::string AuthMessageToString(const DeviceAuthMessage& message) {
   return out;
 }
 
-void CreateAuthChallengeMessage(CastMessage* message_proto) {
+void CreateAuthChallengeMessage(CastMessage* message_proto, std::string nonce) {
   CHECK(message_proto);
   DeviceAuthMessage auth_message;
-  auth_message.mutable_challenge();
+  auth_message.mutable_challenge()->set_sender_nonce(nonce);
   std::string auth_message_string;
   auth_message.SerializeToString(&auth_message_string);