Add FilePath::FinalExtension() to avoid double extensions (.tar.gz) for file selector

base/files/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 206 matching lines @@
 
   // Returns a FilePath corresponding to the last path component of this
   // object, either a file or a directory.  If this object already refers to
   // the root directory, returns a FilePath identifying the root directory;
   // this is the only situation in which BaseName will return an absolute path.
   FilePath BaseName() const WARN_UNUSED_RESULT;
 
   // Returns ".jpg" for path "C:\pics\jojo.jpg", or an empty string if
   // the file has no extension.  If non-empty, Extension() will always start
   // with precisely one ".".  The following code should always work regardless
-  // of the value of path.
+  // of the value of path.  For common double-extensions like .tar.gz and
+  // .user.js, this method returns the combined extension.  For a single
+  // component, use FinalExtension().
   // new_path = path.RemoveExtension().value().append(path.Extension());
   // ASSERT(new_path == path.value());
   // NOTE: this is different from the original file_util implementation which
   // returned the extension without a leading "." ("jpg" instead of ".jpg")
   StringType Extension() const;
 
+  // Returns the path's file extension, as in Extension(), but will
+  // never return a double extension.
+  //
+  // TODO(davidben): Check all our extension-sensitive code to see if
+  // we can rename this to Extension() and the other to something like
+  // LongExtension(), defaulting to short extensions and leaving the
+  // long "extensions" to logic like file_util::GetUniquePathNumber().
+  StringType FinalExtension() const;
+
   // Returns "C:\pics\jojo" for path "C:\pics\jojo.jpg"
   // NOTE: this is slightly different from the similar file_util implementation
   // which returned simply 'jojo'.
   FilePath RemoveExtension() const WARN_UNUSED_RESULT;
 
+  // Removes the path's file extension, as in RemoveExtension(), but
+  // ignores double extensions.
+  FilePath RemoveFinalExtension() const WARN_UNUSED_RESULT;
+
   // Inserts |suffix| after the file name portion of |path| but before the
   // extension.  Returns "" if BaseName() == "." or "..".
   // 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(
@@ skipping 191 matching lines @@
 
 inline size_t hash_value(const base::FilePath& f) {
   return hash_value(f.value());
 }
 
 #endif  // COMPILER
 
 }  // namespace BASE_HASH_NAMESPACE
 
 #endif  // BASE_FILES_FILE_PATH_H_