Support more configurability in GN toolchains

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 681ee2ff4199b6a1e2d6b5945258fb413f5ab76c..12fc5ac5ea98dad5fdafbc7d91e190e6155f53a6 100644
--- a/tools/gn/path_output.h
+++ b/tools/gn/path_output.h
@@ -50,6 +50,11 @@ class PathOutput {
   void WriteFile(std::ostream& out, const OutputFile& file) const;
   void WriteFile(std::ostream& out, const base::FilePath& file) const;
 
+  // Writes the given OutputFiles with spaces separating them. This will also
+  // write an initial space before the first item.
+  void WriteFiles(std::ostream& out,
+                  const std::vector<OutputFile>& files) const;
+
   // This variant assumes the dir ends in a trailing slash or is empty.
   void WriteDir(std::ostream& out,
                 const SourceDir& dir,