Standardize usage of virtual/override/final in mojo/

mojo/public/cpp/utility/tests/thread_unittest.cc

Index: mojo/public/cpp/utility/tests/thread_unittest.cc
diff --git a/mojo/public/cpp/utility/tests/thread_unittest.cc b/mojo/public/cpp/utility/tests/thread_unittest.cc
index 0d81ef8fc35552a22ad755e5b1a1aa74dc084485..57c4ad9b19244bd44a2c40e592b27f79b4785070 100644
--- a/mojo/public/cpp/utility/tests/thread_unittest.cc
+++ b/mojo/public/cpp/utility/tests/thread_unittest.cc
@@ -22,10 +22,9 @@ class SetIntThread : public Thread {
         value_(value) {
   }
 
-  virtual ~SetIntThread() {
-  }
+  ~SetIntThread() override {}
 
-  virtual void Run() override { *int_to_set_ = value_; }
+  void Run() override { *int_to_set_ = value_; }
 
  private:
   int* const int_to_set_;