Hook up symbol files to the Windows GN build.

tools/gn/path_output.h

Index: tools/gn/path_output.h
diff --git a/tools/gn/path_output.h b/tools/gn/path_output.h
index ba4a5f60738e12e830a56ecd9f4470d6aa25ddc0..681ee2ff4199b6a1e2d6b5945258fb413f5ab76c 100644
--- a/tools/gn/path_output.h
+++ b/tools/gn/path_output.h
@@ -49,10 +49,16 @@ class PathOutput {
   void WriteFile(std::ostream& out, const SourceFile& file) const;
   void WriteFile(std::ostream& out, const OutputFile& file) const;
   void WriteFile(std::ostream& out, const base::FilePath& file) const;
+
+  // This variant assumes the dir ends in a trailing slash or is empty.
   void WriteDir(std::ostream& out,
                 const SourceDir& dir,
                 DirSlashEnding slash_ending) const;
 
+  void WriteDir(std::ostream& out,
+                const OutputFile& file,
+                DirSlashEnding slash_ending) const;
+
   // Backend for WriteFile and WriteDir. This appends the given file or
   // directory string to the file.
   void WritePathStr(std::ostream& out, const base::StringPiece& str) const;