Setting "SubSystem" option on "Link" page for Visual Studio project.

tools/gn/visual_studio_utils.h

 // 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.
 
 #ifndef TOOLS_GN_VISUAL_STUDIO_UTILS_H_
 #define TOOLS_GN_VISUAL_STUDIO_UTILS_H_
 
 #include <string>
 
 // Some compiler options which will be written to project file. We don't need to
 // specify all options because generated project file is going to be used only
 // for compilation of single file. For real build ninja files are used.
 struct CompilerOptions {
   CompilerOptions();
   ~CompilerOptions();
 
   std::string additional_options;
   std::string buffer_security_check;
   std::string forced_include_files;
   std::string disable_specific_warnings;
   std::string optimization;
   std::string runtime_library;
   std::string treat_warning_as_error;
   std::string warning_level;
 };
 
+// Some linker options which will be written to project file. We don't need to
+// specify all options because generated project file is going to be used only
+// for compilation of single file. For real build ninja files are used.
+struct LinkerOptions {
+  LinkerOptions();
+  ~LinkerOptions();
+
+  std::string subsystem;
+};
+
 // Generates something which looks like a GUID, but depends only on the name and
 // seed. This means the same name / seed will always generate the same GUID, so
 // that projects and solutions which refer to each other can explicitly
 // determine the GUID to refer to explicitly. It also means that the GUID will
 // not change when the project for a target is rebuilt.
 std::string MakeGuid(const std::string& entry_path, const std::string& seed);
 
 // Parses |cflag| value and stores it in |options|.
 void ParseCompilerOption(const std::string& cflag, CompilerOptions* options);
 
+// Parses |ldflags| value and stores it in |options|.
+void ParseLinkerOption(const std::string& ldflag, LinkerOptions* options);
+
 #endif  // TOOLS_GN_VISUAL_STUDIO_UTILS_H_