Standardize usage of virtual/override/final in mojo/

mojo/apps/js/mojo_runner_delegate.h

Index: mojo/apps/js/mojo_runner_delegate.h
diff --git a/mojo/apps/js/mojo_runner_delegate.h b/mojo/apps/js/mojo_runner_delegate.h
index 8a7b448bc167704bf27a93fe04d4432f9b938f42..ddc95989539e9eaef32b66891e88fa42ccf8dc3f 100644
--- a/mojo/apps/js/mojo_runner_delegate.h
+++ b/mojo/apps/js/mojo_runner_delegate.h
@@ -15,14 +15,14 @@ namespace apps {
 class MojoRunnerDelegate : public gin::ModuleRunnerDelegate {
  public:
   MojoRunnerDelegate();
-  virtual ~MojoRunnerDelegate();
+  ~MojoRunnerDelegate() override;
 
   void Start(gin::Runner* runner, MojoHandle pipe, const std::string& module);
 
  private:
   // From ModuleRunnerDelegate:
-  virtual void UnhandledException(gin::ShellRunner* runner,
-                                  gin::TryCatch& try_catch) override;
+  void UnhandledException(gin::ShellRunner* runner,
+                          gin::TryCatch& try_catch) override;
 
   DISALLOW_COPY_AND_ASSIGN(MojoRunnerDelegate);
 };