Implement tracking of BUILD.gn files used to define target, toolchain or

tools/gn/input_file.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_INPUT_FILE_H_
 #define TOOLS_GN_INPUT_FILE_H_
 
 #include <string>
 
+#include "base/containers/flat_set.h"
 #include "base/files/file_path.h"
 #include "base/logging.h"
 #include "base/macros.h"
 #include "tools/gn/source_dir.h"
 #include "tools/gn/source_file.h"
 
 class InputFile {
  public:
   explicit InputFile(const SourceFile& name);
 
@@ skipping 35 matching lines @@
 
   base::FilePath physical_name_;
   std::string friendly_name_;
 
   bool contents_loaded_;
   std::string contents_;
 
   DISALLOW_COPY_AND_ASSIGN(InputFile);
 };
 
+using InputFileSet = base::flat_set<const InputFile*>;
+
 #endif  // TOOLS_GN_INPUT_FILE_H_