Update from https://crrev.com/312398

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 220 matching lines @@
   // 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.  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;
+  StringType Extension() const WARN_UNUSED_RESULT;
 
   // 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 base::GetUniquePathNumber().
-  StringType FinalExtension() const;
+  StringType FinalExtension() const WARN_UNUSED_RESULT;
 
   // 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;
 
@@ skipping 196 matching lines @@
 template<>
 struct hash<base::FilePath> {
   size_t operator()(const base::FilePath& f) const {
     return hash<base::FilePath::StringType>()(f.value());
   }
 };
 
 }  // namespace BASE_HASH_NAMESPACE
 
 #endif  // BASE_FILES_FILE_PATH_H_