Add optional public header checking to GN build

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 <string>
 
 #include "base/files/file_path.h"
@@ skipping 10 matching lines @@
   SOURCE_ASM,
   SOURCE_C,
   SOURCE_CC,
   SOURCE_H,
   SOURCE_M,
   SOURCE_MM,
   SOURCE_S,
   SOURCE_RC,
 };
 
-SourceFileType GetSourceFileType(const SourceFile& file,
-                                 Settings::TargetOS os);
+SourceFileType GetSourceFileType(const SourceFile& file);
 
 // Returns the extension, not including the dot, for the given file type on the
 // given system.
 //
 // Some targets make multiple files (like a .dll and an import library). This
 // function returns the name of the file other targets should depend on and
 // link to (so in this example, the import library).
 const char* GetExtensionForOutputType(Target::OutputType type,
                                       Settings::TargetOS os);
 
@@ skipping 127 matching lines @@
 SourceDir GetOutputDirForSourceDir(const Settings* settings,
                                    const SourceDir& source_dir);
 SourceDir GetGenDirForSourceDir(const Settings* settings,
                                 const SourceDir& source_dir);
 SourceDir GetTargetOutputDir(const Target* target);
 SourceDir GetTargetGenDir(const Target* target);
 SourceDir GetCurrentOutputDir(const Scope* scope);
 SourceDir GetCurrentGenDir(const Scope* scope);
 
 #endif  // TOOLS_GN_FILESYSTEM_UTILS_H_