GN: toolchain threading cleanup

tools/gn/ninja_script_target_writer.h

Index: tools/gn/ninja_script_target_writer.h
diff --git a/tools/gn/ninja_script_target_writer.h b/tools/gn/ninja_script_target_writer.h
index e84d618ad58960cadca63e665dc421cf8fc0335b..9c51a6a64f356c0555f8a48964e8bf9ce4b46456 100644
--- a/tools/gn/ninja_script_target_writer.h
+++ b/tools/gn/ninja_script_target_writer.h
@@ -17,7 +17,9 @@ class OutputFile;
 // Writes a .ninja file for a custom script target type.
 class NinjaScriptTargetWriter : public NinjaTargetWriter {
  public:
-  NinjaScriptTargetWriter(const Target* target, std::ostream& out);
+  NinjaScriptTargetWriter(const Target* target,
+                          const Toolchain* toolchain,
+                          std::ostream& out);
   virtual ~NinjaScriptTargetWriter();
 
   virtual void Run() OVERRIDE;