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

tools/gn/ninja_binary_target_writer.h

Index: tools/gn/ninja_binary_target_writer.h
diff --git a/tools/gn/ninja_binary_target_writer.h b/tools/gn/ninja_binary_target_writer.h
index e3236ce52f6f65a896e845a8a3646127dcb5d7ce..49e56e757f56a211c4c5aa0363903a60ad970f17 100644
--- a/tools/gn/ninja_binary_target_writer.h
+++ b/tools/gn/ninja_binary_target_writer.h
@@ -18,9 +18,9 @@ struct EscapeOptions;
 class NinjaBinaryTargetWriter : public NinjaTargetWriter {
  public:
   NinjaBinaryTargetWriter(const Target* target, std::ostream& out);
-  virtual ~NinjaBinaryTargetWriter();
+  ~NinjaBinaryTargetWriter() override;
 
-  virtual void Run() OVERRIDE;
+  void Run() OVERRIDE;
 
  private:
   typedef std::set<OutputFile> OutputFileSet;