Standardize usage of virtual/override/final in mojo/

mojo/public/cpp/bindings/lib/router.cc

Index: mojo/public/cpp/bindings/lib/router.cc
diff --git a/mojo/public/cpp/bindings/lib/router.cc b/mojo/public/cpp/bindings/lib/router.cc
index 91a5d31c59929d25b6d258e229a55e9a02ad0150..bb29e47c1c83a2d434f6b0976ed5c2d7aeecb1fe 100644
--- a/mojo/public/cpp/bindings/lib/router.cc
+++ b/mojo/public/cpp/bindings/lib/router.cc
@@ -15,10 +15,10 @@ class ResponderThunk : public MessageReceiver {
  public:
   explicit ResponderThunk(const SharedData<Router*>& router)
       : router_(router) {}
-  virtual ~ResponderThunk() {}
+  ~ResponderThunk() override {}
 
   // MessageReceiver implementation:
-  virtual bool Accept(Message* message) override {
+  bool Accept(Message* message) override {
     MOJO_DCHECK(message->has_flag(kMessageIsResponse));
 
     bool result = false;