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

tools/gn/ninja_copy_target_writer.h

Index: tools/gn/ninja_copy_target_writer.h
diff --git a/tools/gn/ninja_copy_target_writer.h b/tools/gn/ninja_copy_target_writer.h
index 58003dc92cc0670164d4689b3d31d97641722ba8..83e5e51abfc8f950770f36dd92a5578cccd81aee 100644
--- a/tools/gn/ninja_copy_target_writer.h
+++ b/tools/gn/ninja_copy_target_writer.h
@@ -14,9 +14,9 @@ class Tool;
 class NinjaCopyTargetWriter : public NinjaTargetWriter {
  public:
   NinjaCopyTargetWriter(const Target* target, std::ostream& out);
-  virtual ~NinjaCopyTargetWriter();
+  ~NinjaCopyTargetWriter() override;
 
-  virtual void Run() OVERRIDE;
+  void Run() OVERRIDE;
 
  private:
   // Writes the rules top copy the file(s), putting the computed output file