Using override keyword in ObjectVisitor class hierarchy.

src/api.cc

 // Copyright 2012 the V8 project 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 "src/api.h"
 
 #include <string.h>  // For memcpy, strlen.
 #ifdef V8_USE_ADDRESS_SANITIZER
 #include <sanitizer/asan_interface.h>
 #endif  // V8_USE_ADDRESS_SANITIZER
@@ skipping 7600 matching lines @@
 void Isolate::VisitExternalResources(ExternalResourceVisitor* visitor) {
   i::Isolate* isolate = reinterpret_cast<i::Isolate*>(this);
   isolate->heap()->VisitExternalResources(visitor);
 }
 
 
 class VisitorAdapter : public i::ObjectVisitor {
  public:
   explicit VisitorAdapter(PersistentHandleVisitor* visitor)
       : visitor_(visitor) {}
-  virtual void VisitPointers(i::Object** start, i::Object** end) {
+  void VisitPointers(i::Object** start, i::Object** end) override {
     UNREACHABLE();
   }
-  virtual void VisitEmbedderReference(i::Object** p, uint16_t class_id) {
+  void VisitEmbedderReference(i::Object** p, uint16_t class_id) override {
     Value* value = ToApi<Value>(i::Handle<i::Object>(p));
     visitor_->VisitPersistentHandle(
         reinterpret_cast<Persistent<Value>*>(&value), class_id);
   }
 
  private:
   PersistentHandleVisitor* visitor_;
 };
 
 
@@ skipping 884 matching lines @@
   Address callback_address =
       reinterpret_cast<Address>(reinterpret_cast<intptr_t>(callback));
   VMState<EXTERNAL> state(isolate);
   ExternalCallbackScope call_scope(isolate, callback_address);
   callback(info);
 }
 
 
 }  // namespace internal
 }  // namespace v8