Minor fixes to tools/gn.

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_SUBSTITUTION_LIST_H_
 #define TOOLS_GN_SUBSTITUTION_LIST_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 12 matching lines @@
              Err* err);
 
   // Makes a SubstitutionList from the given hardcoded patterns.
   static SubstitutionList MakeForTest(
       const char* a,
       const char* b = nullptr,
       const char* c = nullptr);
 
   const std::vector<SubstitutionPattern>& list() const { return list_; }
 
-  // Returns a list of all substitution types used by the patterns in thist
+  // Returns a list of all substitution types used by the patterns in this
   // list, with the exception of LITERAL.
   const std::vector<SubstitutionType>& required_types() const {
     return required_types_;
   }
 
   void FillRequiredTypes(SubstitutionBits* bits) const;
 
  private:
   std::vector<SubstitutionPattern> list_;
 
   std::vector<SubstitutionType> required_types_;
 };
 
 #endif  // TOOLS_GN_SUBSTITUTION_LIST_H_