Fix Windows cast warning for GN unit test.

tools/gn/command_args.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 <stdio.h>
 #include <stdlib.h>
 
 #include <map>
 
 #include "base/command_line.h"
@@ skipping 236 matching lines @@
           "# Build arguments go here. Examples:\n"
           "#   enable_doom_melon = true\n"
           "#   crazy_something = \"absolutely\"\n";
 #if defined(OS_WIN)
       // Use Windows lineendings for this file since it will often open in
       // Notepad which can't handle Unix ones.
       ReplaceSubstringsAfterOffset(&argfile_default_contents, 0, "\n", "\r\n");
 #endif
       base::CreateDirectory(arg_file.DirName());
       base::WriteFile(arg_file, argfile_default_contents.c_str(),
-                      argfile_default_contents.size());
+                      static_cast<int>(argfile_default_contents.size()));
     }
 
     ScopedTrace editor_trace(TraceItem::TRACE_SETUP, "Waiting for editor");
     if (!RunEditor(arg_file))
       return 1;
   }
 
   // Now do a normal "gen" command.
   OutputString("Generating files...\n");
   std::vector<std::string> gen_commands;
@@ skipping 70 matching lines @@
         "Or see \"gn help args\" for more variants.").PrintToStdout();
     return 1;
   }
 
   if (base::CommandLine::ForCurrentProcess()->HasSwitch(kSwitchList))
     return ListArgs(args[0]);
   return EditArgsFile(args[0]);
 }
 
 }  // namespace commands