Convert OVERRIDE -> override and update virtual/final usage in tools/gn/.

tools/gn/ninja_group_target_writer.h

Index: tools/gn/ninja_group_target_writer.h
diff --git a/tools/gn/ninja_group_target_writer.h b/tools/gn/ninja_group_target_writer.h
index f355539be3e902ada9ffb279748ce1676807f977..66e5f04315526f37e9090abe3750330059f71729 100644
--- a/tools/gn/ninja_group_target_writer.h
+++ b/tools/gn/ninja_group_target_writer.h
@@ -5,16 +5,16 @@
 #ifndef TOOLS_GN_NINJA_GROUP_TARGET_WRITER_H_
 #define TOOLS_GN_NINJA_GROUP_TARGET_WRITER_H_
 
-#include "base/compiler_specific.h"
+#include "base/macros.h"
 #include "tools/gn/ninja_target_writer.h"
 
 // Writes a .ninja file for a group target type.
 class NinjaGroupTargetWriter : public NinjaTargetWriter {
  public:
   NinjaGroupTargetWriter(const Target* target, std::ostream& out);
-  virtual ~NinjaGroupTargetWriter();
+  ~NinjaGroupTargetWriter() override;
 
-  virtual void Run() override;
+  void Run() override;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(NinjaGroupTargetWriter);