Standardize usage of virtual/override/final in mojo/

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

Index: mojo/public/cpp/utility/tests/mutex_unittest.cc
diff --git a/mojo/public/cpp/utility/tests/mutex_unittest.cc b/mojo/public/cpp/utility/tests/mutex_unittest.cc
index a95495e076c8f9b02d3b3fd1278930ed1d42d160..d6f75da574a0dbfdb25c62cc8d6e9ad86581d8c5 100644
--- a/mojo/public/cpp/utility/tests/mutex_unittest.cc
+++ b/mojo/public/cpp/utility/tests/mutex_unittest.cc
@@ -111,11 +111,9 @@ class FiddlerThread : public Thread {
       : fiddler_(fiddler) {
   }
 
-  virtual ~FiddlerThread() {
-    delete fiddler_;
-  }
+  ~FiddlerThread() override { delete fiddler_; }
 
-  virtual void Run() override { fiddler_->Fiddle(); }
+  void Run() override { fiddler_->Fiddle(); }
 
  private:
   Fiddler* const fiddler_;
@@ -167,9 +165,9 @@ TEST(MutexTest, ThreadedStress) {
 class TryThread : public Thread {
  public:
   explicit TryThread(Mutex* mutex) : mutex_(mutex), try_lock_succeeded_() {}
-  virtual ~TryThread() {}
+  ~TryThread() override {}
 
-  virtual void Run() override {
+  void Run() override {
     try_lock_succeeded_ = mutex_->TryLock();
     if (try_lock_succeeded_)
       mutex_->Unlock();