Refactor GN source expansions.

tools/gn/command_help.cc

 // 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.
 
 #include <algorithm>
 #include <iostream>
 
 #include "tools/gn/args.h"
 #include "tools/gn/commands.h"
 #include "tools/gn/err.h"
-#include "tools/gn/file_template.h"
 #include "tools/gn/functions.h"
 #include "tools/gn/input_conversion.h"
 #include "tools/gn/pattern.h"
 #include "tools/gn/setup.h"
 #include "tools/gn/standard_out.h"
+#include "tools/gn/substitution_writer.h"
 #include "tools/gn/variables.h"
 
 namespace commands {
 
 namespace {
 
 void PrintToplevelHelp() {
   OutputString("Commands (type \"gn help <command>\" for more details):\n");
 
   const commands::CommandInfoMap& command_map = commands::GetCommands();
@@ skipping 148 matching lines @@
     return 0;
   }
 
   // No help on this.
   Err(Location(), "No help on \"" + args[0] + "\".").PrintToStdout();
   RunHelp(std::vector<std::string>());
   return 1;
 }
 
 }  // namespace commands