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

extensions/browser/api/cast_channel/cast_message_util.h

Index: extensions/browser/api/cast_channel/cast_message_util.h
diff --git a/extensions/browser/api/cast_channel/cast_message_util.h b/extensions/browser/api/cast_channel/cast_message_util.h
index b14b737a5c93b99398e28bea74be27f87919e637..a117cac8eba57f57f4ab86a565b52d0a51bff9bf 100644
--- a/extensions/browser/api/cast_channel/cast_message_util.h
+++ b/extensions/browser/api/cast_channel/cast_message_util.h
@@ -33,7 +33,9 @@ std::string CastMessageToString(const CastMessage& message_proto);
 std::string AuthMessageToString(const DeviceAuthMessage& message);
 
 // Fills |message_proto| appropriately for an auth challenge request message.
-void CreateAuthChallengeMessage(CastMessage* message_proto);
+// Uses the challenge |nonce|.
+void CreateAuthChallengeMessage(CastMessage* message_proto,
+                                const std::string& nonce);
 
 // Returns whether the given message is an auth handshake message.
 bool IsAuthMessage(const CastMessage& message);