Update CastSocket connection flow to check for receiver credentials.

chrome/browser/extensions/api/cast_channel/cast_message_util.h

Index: chrome/browser/extensions/api/cast_channel/cast_message_util.h
===================================================================
--- chrome/browser/extensions/api/cast_channel/cast_message_util.h	(revision 230132)
+++ chrome/browser/extensions/api/cast_channel/cast_message_util.h	(working copy)
@@ -12,6 +12,7 @@
 namespace cast_channel {
 
 class CastMessage;
+class DeviceAuthMessage;
 struct MessageInfo;
 
 // Fills |message_proto| from |message| and returns true on success.
@@ -23,8 +24,17 @@
                               MessageInfo* message);
 
 // Returns a human readable string for |message_proto|.
-const std::string MessageProtoToString(const CastMessage& message_proto);
+std::string CastMessageToString(const CastMessage& message_proto);
 
+// Returns a human readable string for |message|.
+std::string AuthMessageToString(const DeviceAuthMessage& message);
+
+// Fills |message_proto| appropriately for an auth challenge request message.
+void CreateAuthChallengeMessage(CastMessage* message_proto);
+
+// Returns whether the given message is an auth handshake message.
+bool IsAuthMessage(const CastMessage& message);
+
 }  // namespace cast_channel
 }  // namespace api
 }  // namespace extensions