Standardize usage of virtual/override/final in mojo/

mojo/edk/system/message_pipe_dispatcher_unittest.cc

Index: mojo/edk/system/message_pipe_dispatcher_unittest.cc
diff --git a/mojo/edk/system/message_pipe_dispatcher_unittest.cc b/mojo/edk/system/message_pipe_dispatcher_unittest.cc
index 96ca4367d855ff2e02b4f58d67a0a5014d4cf975..ae651fa981d5f7f4caaf236a77f4148789398472 100644
--- a/mojo/edk/system/message_pipe_dispatcher_unittest.cc
+++ b/mojo/edk/system/message_pipe_dispatcher_unittest.cc
@@ -528,10 +528,10 @@ class WriterThread : public base::SimpleThread {
     *bytes_written_ = 0;
   }
 
-  virtual ~WriterThread() { Join(); }
+  ~WriterThread() override { Join(); }
 
  private:
-  virtual void Run() override {
+  void Run() override {
     // Make some data to write.
     unsigned char buffer[kMaxMessageSize];
     for (size_t i = 0; i < kMaxMessageSize; i++)
@@ -581,10 +581,10 @@ class ReaderThread : public base::SimpleThread {
     *bytes_read_ = 0;
   }
 
-  virtual ~ReaderThread() { Join(); }
+  ~ReaderThread() override { Join(); }
 
  private:
-  virtual void Run() override {
+  void Run() override {
     unsigned char buffer[kMaxMessageSize];
     Waiter w;
     HandleSignalsState hss;