Add a warning when developing an extension that uses old manifest version.

chrome/common/extensions/extension_file_util.h

 // Copyright (c) 2012 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_COMMON_EXTENSIONS_EXTENSION_FILE_UTIL_H_
 #define CHROME_COMMON_EXTENSIONS_EXTENSION_FILE_UTIL_H_
 #pragma once
 
 #include <string>
 #include <map>
@@ skipping 49 matching lines @@
                                     std::string* error);
 
 // Returns true if the given extension object is valid and consistent.
 // May also append a series of warning messages to |warnings|, but they
 // should not prevent the extension from running.
 //
 // Otherwise, returns false, and a description of the error is
 // returned in |error|.
 bool ValidateExtension(const extensions::Extension* extension,
                        std::string* error,
-                       std::vector<std::string>* warnings);
+                       extensions::Extension::InstallWarningVector* warnings);
 
 // Returns a list of files that contain private keys inside |extension_dir|.
 std::vector<FilePath> FindPrivateKeyFiles(const FilePath& extension_dir);
 
 // Cleans up the extension install directory. It can end up with garbage in it
 // if extensions can't initially be removed when they are uninstalled (eg if a
 // file is in use).
 //
 // |extensions_dir| is the install directory to look in. |extension_paths| is a
 // map from extension id to full installation path.
@@ skipping 40 matching lines @@
 FilePath GetUserDataTempDir();
 
 // Helper function to delete files. This is used to avoid ugly casts which
 // would be necessary with PostMessage since file_util::Delete is overloaded.
 // TODO(skerner): Make a version of Delete that is not overloaded in file_util.
 void DeleteFile(const FilePath& path, bool recursive);
 
 }  // namespace extension_file_util
 
 #endif  // CHROME_COMMON_EXTENSIONS_EXTENSION_FILE_UTIL_H_