Add an AddExtension() method in FilePath

base/file_path.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.
 
 // FilePath is a container for pathnames stored in a platform's native string
 // type, providing containers for manipulation in according with the
 // platform's conventions for pathnames.  It supports the following path
 // types:
 //
 //                   POSIX            Windows
@@ skipping 224 matching lines @@
   // Examples:
   // path == "C:\pics\jojo.jpg" suffix == " (1)", returns "C:\pics\jojo (1).jpg"
   // path == "jojo.jpg"         suffix == " (1)", returns "jojo (1).jpg"
   // path == "C:\pics\jojo"     suffix == " (1)", returns "C:\pics\jojo (1)"
   // path == "C:\pics.old\jojo" suffix == " (1)", returns "C:\pics.old\jojo (1)"
   FilePath InsertBeforeExtension(
       const StringType& suffix) const WARN_UNUSED_RESULT;
   FilePath InsertBeforeExtensionASCII(
       const base::StringPiece& suffix) const WARN_UNUSED_RESULT;
 
+  // Adds |extension| to |file_name|. Returns the current FilePath if
+  // |extension| is empty. Returns "" if BaseName() == "." or "..".
+  FilePath AddExtension(
+      const StringType& extension) const WARN_UNUSED_RESULT;
+
   // Replaces the extension of |file_name| with |extension|.  If |file_name|
-  // does not have an extension, them |extension| is added.  If |extension| is
+  // does not have an extension, then |extension| is added.  If |extension| is
   // empty, then the extension is removed from |file_name|.
   // Returns "" if BaseName() == "." or "..".
   FilePath ReplaceExtension(
       const StringType& extension) const WARN_UNUSED_RESULT;
 
   // Returns true if the file path matches the specified extension. The test is
   // case insensitive. Don't forget the leading period if appropriate.
   bool MatchesExtension(const StringType& extension) const;
 
   // Returns a FilePath by appending a separator and the supplied path
@@ skipping 163 matching lines @@
 
 inline size_t hash_value(const FilePath& f) {
   return hash_value(f.value());
 }
 
 #endif  // COMPILER
 
 }  // namespace BASE_HASH_NAMESPACE
 
 #endif  // BASE_FILE_PATH_H_