Standardize usage of virtual/override/final in mojo/

mojo/services/html_viewer/webthread_impl.cc

Index: mojo/services/html_viewer/webthread_impl.cc
diff --git a/mojo/services/html_viewer/webthread_impl.cc b/mojo/services/html_viewer/webthread_impl.cc
index 678d22e77f8ce0d8899344476abf9db800fd9685..8c2425a67de9234bdea584c09e9dcffc3091719c 100644
--- a/mojo/services/html_viewer/webthread_impl.cc
+++ b/mojo/services/html_viewer/webthread_impl.cc
@@ -24,11 +24,11 @@ class WebThreadBase::TaskObserverAdapter
   TaskObserverAdapter(WebThread::TaskObserver* observer)
       : observer_(observer) {}
 
-  virtual void WillProcessTask(const base::PendingTask& pending_task) override {
+  void WillProcessTask(const base::PendingTask& pending_task) override {
     observer_->willProcessTask();
   }
 
-  virtual void DidProcessTask(const base::PendingTask& pending_task) override {
+  void DidProcessTask(const base::PendingTask& pending_task) override {
     observer_->didProcessTask();
   }