Cleanup remaining class/struct fwd declarations

tools/gn/filesystem_utils.h

 // Copyright (c) 2013 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 TOOLS_GN_FILESYSTEM_UTILS_H_
 #define TOOLS_GN_FILESYSTEM_UTILS_H_
 
 #include <stddef.h>
 
 #include <string>
 
 #include "base/files/file_path.h"
 #include "base/strings/string_piece.h"
 #include "tools/gn/settings.h"
 #include "tools/gn/target.h"
 
 class Err;
-class Location;
-class Value;
 
 std::string FilePathToUTF8(const base::FilePath::StringType& str);
 inline std::string FilePathToUTF8(const base::FilePath& path) {
   return FilePathToUTF8(path.value());
 }
 base::FilePath UTF8ToFilePath(const base::StringPiece& sp);
 
 // Extensions -----------------------------------------------------------------
 
 // Returns the index of the extension (character after the last dot not after a
@@ skipping 232 matching lines @@
 OutputFile GetBuildDirForTargetAsOutputFile(const Target* target,
                                             BuildDirType type);
 
 // Returns the scope's current directory.
 SourceDir GetScopeCurrentBuildDirAsSourceDir(const Scope* scope,
                                              BuildDirType type);
 // Lack of OutputDir version is due only to it not currently being needed,
 // please add one if you need it.
 
 #endif  // TOOLS_GN_FILESYSTEM_UTILS_H_