Support more configurability in GN toolchains

tools/gn/substitution_list.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_SUBSTUTITION_LIST_H
 #define TOOLS_GN_SUBSTUTITION_LIST_H
 
 #include <string>
 #include <vector>
 
@@ skipping 17 matching lines @@
       const char* c = NULL);
 
   const std::vector<SubstitutionPattern>& list() const { return list_; }
 
   // Returns a list of all substitution types used by the patterns in thist
   // list, with the exception of LITERAL.
   const std::vector<SubstitutionType>& required_types() const {
     return required_types_;
   }
 
+  void FillRequiredTypes(SubstitutionBits* bits) const;
+
  private:
-  void FillRequiredTypes();
-
   std::vector<SubstitutionPattern> list_;
 
   std::vector<SubstitutionType> required_types_;
 };
 
 #endif  // TOOLS_GN_SUBSTUTITION_LIST_H