[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 5d4e9ff834c52e80ed26c2e31991bcbd8f1595e6..0f4d952991e9785e31d98ac81cfd0c38b5880522 100644
--- a/extensions/browser/api/cast_channel/cast_message_util.cc
+++ b/extensions/browser/api/cast_channel/cast_message_util.cc
@@ -9,6 +9,7 @@
 #include "base/logging.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/values.h"
+#include "extensions/browser/api/cast_channel/cast_auth_util.h"
 #include "extensions/common/api/cast_channel.h"
 #include "extensions/common/api/cast_channel/cast_channel.pb.h"
 
@@ -134,10 +135,11 @@ std::string AuthMessageToString(const DeviceAuthMessage& message) {
   return out;
 }
 
-void CreateAuthChallengeMessage(CastMessage* message_proto) {
+void CreateAuthChallengeMessage(CastMessage* message_proto,
+                                const AuthContext& auth_context) {
   CHECK(message_proto);
   DeviceAuthMessage auth_message;
-  auth_message.mutable_challenge();
+  auth_message.mutable_challenge()->set_sender_nonce(auth_context.nonce());
   std::string auth_message_string;
   auth_message.SerializeToString(&auth_message_string);