GN support for generating VS2013 project files

tools/gn/visual_studio_writer.h

Index: tools/gn/visual_studio_writer.h
diff --git a/tools/gn/visual_studio_writer.h b/tools/gn/visual_studio_writer.h
index bd94f929b7e50214eea0a49f6012f0585e39ad7a..040922054a0e210c7164ab9ea9f343a5d247a071 100644
--- a/tools/gn/visual_studio_writer.h
+++ b/tools/gn/visual_studio_writer.h
@@ -23,9 +23,15 @@ class Target;
 
 class VisualStudioWriter {
  public:
+  enum Version {
+    Vs2013 = 1,  // Visual Studio 2013
+    Vs2015       // Visual Studio 2015
+  };
+
   // On failure will populate |err| and will return false.
   static bool RunAndWriteFiles(const BuildSettings* build_settings,
                                Builder* builder,
+                               Version version,
                                Err* err);
 
  private:
@@ -67,7 +73,8 @@ class VisualStudioWriter {
   using SolutionProjects = std::vector<SolutionProject*>;
   using SolutionFolders = std::vector<SolutionEntry*>;
 
-  explicit VisualStudioWriter(const BuildSettings* build_settings);
+  explicit VisualStudioWriter(const BuildSettings* build_settings,
+                              Version version);
   ~VisualStudioWriter();
 
   bool WriteProjectFiles(const Target* target, Err* err);
@@ -86,6 +93,15 @@ class VisualStudioWriter {
 
   const BuildSettings* build_settings_;
 
+  // Toolset version.
+  const char* toolset_version_;
+
+  // Project version.
+  const char* project_version_;
+
+  // Visual Studio version string.
+  const char* version_string_;
+
   // Indicates if project files are generated for Debug mode configuration.
   bool is_debug_config_;