Update {virtual,override} to follow C++11 style in base.

base/observer_list_unittest.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "base/observer_list.h"
 #include "base/observer_list_threadsafe.h"
 
 #include <vector>
 
 #include "base/compiler_specific.h"
@@ skipping 53 matching lines @@
 
 template <typename ObserverListType>
 class AddInObserve : public Foo {
  public:
   explicit AddInObserve(ObserverListType* observer_list)
       : added(false),
         observer_list(observer_list),
         adder(1) {
   }
 
-  virtual void Observe(int x) override {
+  void Observe(int x) override {
     if (!added) {
       added = true;
       observer_list->AddObserver(&adder);
     }
   }
 
   bool added;
   ObserverListType* observer_list;
   Adder adder;
 };
@@ skipping 449 matching lines @@
   ListDestructor a(observer_list);
   observer_list->AddObserver(&a);
 
   FOR_EACH_OBSERVER(Foo, *observer_list, Observe(0));
   // If this test fails, there'll be Valgrind errors when this function goes out
   // of scope.
 }
 
 }  // namespace
 }  // namespace base