Update CastSocket connection flow to check for receiver credentials.

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

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_EXTENSIONS_API_CAST_CHANNEL_CAST_MESSAGE_UTIL_H_
 #define CHROME_BROWSER_EXTENSIONS_API_CAST_CHANNEL_CAST_MESSAGE_UTIL_H_
 
 #include <string>
 
 namespace extensions {
 namespace api {
 namespace cast_channel {
 
 class CastMessage;
+class DeviceAuthMessage;
 struct MessageInfo;
 
 // Fills |message_proto| from |message| and returns true on success.
 bool MessageInfoToCastMessage(const MessageInfo& message,
                               CastMessage* message_proto);
 
 // Fills |message| from |message_proto| and returns true on success.
 bool CastMessageToMessageInfo(const CastMessage& message_proto,
                               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
 
 #endif  // CHROME_BROWSER_EXTENSIONS_API_CAST_CHANNEL_CAST_MESSAGE_UTIL_H_