Using override keyword in ObjectVisitor class hierarchy.

test/cctest/test-global-handles.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 57 matching lines @@
 
   virtual const char* GetLabel() { return "whatever"; }
 
  private:
   bool has_been_disposed_;
 };
 
 
 class TestObjectVisitor : public ObjectVisitor {
  public:
-  virtual void VisitPointers(Object** start, Object** end) {
+  void VisitPointers(Object** start, Object** end) override {
     for (Object** o = start; o != end; ++o)
       visited.Add(*o);
   }
 
   List<Object*> visited;
 };
 
 
 TEST(IterateObjectGroupsOldApi) {
   CcTest::InitializeVM();
@@ skipping 301 matching lines @@
   v8::Local<v8::Object> o = v8::Object::New(isolate);
   CHECK(!o.IsEmpty());
   v8::Persistent<v8::Object> p(isolate, o);
   CHECK(o == p.Get(isolate));
   CHECK(v8::Local<v8::Object>::New(isolate, p) == p.Get(isolate));
 
   v8::Global<v8::Object> g(isolate, o);
   CHECK(o == g.Get(isolate));
   CHECK(v8::Local<v8::Object>::New(isolate, g) == g.Get(isolate));
 }