Standardize usage of virtual/override/final in mojo/

mojo/edk/system/waiter_unittest.cc

Index: mojo/edk/system/waiter_unittest.cc
diff --git a/mojo/edk/system/waiter_unittest.cc b/mojo/edk/system/waiter_unittest.cc
index bbbc5b8081efa16a3ca2251f104c26253def9068..859ff0d7056394e7f3490e6aa5dd99259d0fc9ab 100644
--- a/mojo/edk/system/waiter_unittest.cc
+++ b/mojo/edk/system/waiter_unittest.cc
@@ -37,7 +37,7 @@ class WaitingThread : public base::SimpleThread {
     waiter_.Init();
   }
 
-  virtual ~WaitingThread() { Join(); }
+  ~WaitingThread() override { Join(); }
 
   void WaitUntilDone(MojoResult* result,
                      uint32_t* context,
@@ -61,7 +61,7 @@ class WaitingThread : public base::SimpleThread {
   Waiter* waiter() { return &waiter_; }
 
  private:
-  virtual void Run() override {
+  void Run() override {
     test::Stopwatch stopwatch;
     MojoResult result;
     uint32_t context = static_cast<uint32_t>(-1);