Using override keyword in ObjectVisitor class hierarchy.

test/cctest/test-heap.cc

 // Copyright 2012 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 4457 matching lines @@
   // Verify that the pointers in the large object got updated.
   for (int i = 0; i < kSize; i += kStep) {
     CHECK_EQ(lo->get(i), *lit);
     CHECK(lo->get(i) != old_location);
   }
 }
 
 
 class DummyVisitor : public ObjectVisitor {
  public:
-  void VisitPointers(Object** start, Object** end) { }
+  void VisitPointers(Object** start, Object** end) override {}
 };
 
 
 TEST(DeferredHandles) {
   CcTest::InitializeVM();
   Isolate* isolate = CcTest::i_isolate();
   Heap* heap = isolate->heap();
   v8::HandleScope scope(reinterpret_cast<v8::Isolate*>(isolate));
   HandleScopeData* data = isolate->handle_scope_data();
   Handle<Object> init(heap->empty_string(), isolate);
@@ skipping 1795 matching lines @@
   isolate->IncrementJsCallsFromApiCounter();
   isolate->IncrementJsCallsFromApiCounter();
   isolate->IncrementJsCallsFromApiCounter();
   calls_per_ms = memory_reducer->SampleAndGetJsCallsPerMs(4);
   CheckDoubleEquals(2, calls_per_ms);
 }
 
 
 }  // namespace internal
 }  // namespace v8