Standardize usage of virtual/override/final in tools/gn/

tools/gn/ninja_action_target_writer.h

Index: tools/gn/ninja_action_target_writer.h
diff --git a/tools/gn/ninja_action_target_writer.h b/tools/gn/ninja_action_target_writer.h
index ac35b5b66477ce7f59c016c17596285d3ecb0e1b..a3c0f7ca309fb5165067b0183459998d83b61ad4 100644
--- a/tools/gn/ninja_action_target_writer.h
+++ b/tools/gn/ninja_action_target_writer.h
@@ -17,9 +17,9 @@ class OutputFile;
 class NinjaActionTargetWriter : public NinjaTargetWriter {
  public:
   NinjaActionTargetWriter(const Target* target, std::ostream& out);
-  virtual ~NinjaActionTargetWriter();
+  ~NinjaActionTargetWriter() override;
 
-  virtual void Run() OVERRIDE;
+  void Run() OVERRIDE;
 
  private:
   FRIEND_TEST_ALL_PREFIXES(NinjaActionTargetWriter,