Fix Visual Studio warning on single file compilation

tools/gn/visual_studio_writer.cc

 // Copyright 2016 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 "tools/gn/visual_studio_writer.h"
 
 #include <algorithm>
 #include <iterator>
 #include <map>
 #include <memory>
@@ skipping 414 matching lines @@
   project.SubElement("PropertyGroup", XmlAttributes("Label", "UserMacros"));
 
   {
     std::unique_ptr<XmlElementWriter> properties =
         project.SubElement("PropertyGroup");
     {
       std::unique_ptr<XmlElementWriter> out_dir =
           properties->SubElement("OutDir");
       path_output.WriteDir(out_dir->StartContent(false),
                            build_settings_->build_dir(),
-                           PathOutput::DIR_NO_LAST_SLASH);
+                           PathOutput::DIR_INCLUDE_LAST_SLASH);
     }
     properties->SubElement("TargetName")->Text("$(ProjectName)");
     if (target->output_type() != Target::GROUP) {
       properties->SubElement("TargetPath")
           ->Text("$(OutDir)\\$(ProjectName)$(TargetExt)");
     }
   }
 
   {
     std::unique_ptr<XmlElementWriter> item_definitions =
@@ skipping 354 matching lines @@
   }
 }
 
 std::string VisualStudioWriter::GetNinjaTarget(const Target* target) {
   std::ostringstream ninja_target_out;
   DCHECK(!target->dependency_output_file().value().empty());
   ninja_path_output_.WriteFile(ninja_target_out,
                                target->dependency_output_file());
   return ninja_target_out.str();
 }