GN flag to fail for unused build args.

tools/gn/switches.h

 // Copyright 2014 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_SWITCHES_H_
 #define TOOLS_GN_SWITCHES_H_
 
 #include <map>
 
 #include "base/strings/string_piece.h"
@@ skipping 22 matching lines @@
 extern const char kArgs_Help[];
 
 extern const char kColor[];
 extern const char kColor_HelpShort[];
 extern const char kColor_Help[];
 
 extern const char kDotfile[];
 extern const char kDotfile_HelpShort[];
 extern const char kDotfile_Help[];
 
+extern const char kFailOnUnusedArgs[];
+extern const char kFailOnUnusedArgs_HelpShort[];
+extern const char kFailOnUnusedArgs_Help[];
+
 extern const char kMarkdown[];
 extern const char kMarkdown_HelpShort[];
 extern const char kMarkdown_Help[];
 
 extern const char kNoColor[];
 extern const char kNoColor_HelpShort[];
 extern const char kNoColor_Help[];
 
 extern const char kQuiet[];
 extern const char kQuiet_HelpShort[];
@@ skipping 23 matching lines @@
 extern const char kVerbose_HelpShort[];
 extern const char kVerbose_Help[];
 
 extern const char kVersion[];
 extern const char kVersion_HelpShort[];
 extern const char kVersion_Help[];
 
 }  // namespace switches
 
 #endif  // TOOLS_GN_SWITCHES_H_