Add a target in GN that generates a last_change.h file for the SVN revision.

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"
@@ skipping 33 matching lines @@
   PrintShortHelp(
       "--root: Specifies source root (overrides .gn file).");
   PrintShortHelp(
       "--secondary: Specifies secondary source root (overrides .gn file).");
   PrintShortHelp(
       "--time: Outputs a summary of how long everything took.");
   PrintShortHelp(
       "--tracelog: Writes a Chrome-compatible trace log to the given file.");
   PrintShortHelp(
       "-v: Verbose mode, print lots of logging.");
+  PrintShortHelp(
+      "--version: Print the GN binary's version and exit.");
 
   // Functions.
   OutputString("\nBuildfile functions (type \"gn help <function>\" for more "
                "details):\n");
   const functions::FunctionInfoMap& function_map = functions::GetFunctions();
   std::vector<std::string> sorted_functions;
   for (functions::FunctionInfoMap::const_iterator i = function_map.begin();
        i != function_map.end(); ++i)
     sorted_functions.push_back(i->first.as_string());
   std::sort(sorted_functions.begin(), sorted_functions.end());
@@ skipping 103 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