Revert of [cast_channel] Move cast_channel related files from //extensions to //components

extensions/browser/api/cast_channel/cast_message_util.h

 // Copyright 2014 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 EXTENSIONS_BROWSER_API_CAST_CHANNEL_CAST_MESSAGE_UTIL_H_
 #define EXTENSIONS_BROWSER_API_CAST_CHANNEL_CAST_MESSAGE_UTIL_H_
 
 #include <string>
 
-namespace cast_channel {
-class CastMessage;
-}  // namespace cast_channel
-
 namespace extensions {
 namespace api {
 namespace cast_channel {
 
+class AuthContext;
+class CastMessage;
+class DeviceAuthMessage;
 struct MessageInfo;
 
 // Fills |message_proto| from |message| and returns true on success.
 bool MessageInfoToCastMessage(const MessageInfo& message,
-                              ::cast_channel::CastMessage* message_proto);
+                              CastMessage* message_proto);
+
+// Checks if the contents of |message_proto| are valid.
+bool IsCastMessageValid(const CastMessage& message_proto);
 
 // Fills |message| from |message_proto| and returns true on success.
-bool CastMessageToMessageInfo(const ::cast_channel::CastMessage& message_proto,
+bool CastMessageToMessageInfo(const CastMessage& message_proto,
                               MessageInfo* message);
 
+// Returns a human readable string for |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.
+// Uses the nonce challenge in |auth_context|.
+void CreateAuthChallengeMessage(CastMessage* message_proto,
+                                const AuthContext& auth_context);
+
+// Returns whether the given message is an auth handshake message.
+bool IsAuthMessage(const CastMessage& message);
+
 }  // namespace cast_channel
 }  // namespace api
 }  // namespace extensions
 
 #endif  // EXTENSIONS_BROWSER_API_CAST_CHANNEL_CAST_MESSAGE_UTIL_H_