Use After Free in crypto.randomFill

We can trigger Use-After-Free while running crypto.randomFill, so we can easily read/write heap memory using a typed array pointing a freed backing store.

void RandomBytesBuffer(const FunctionCallbackInfo<Value>& args) {
...
  char* data = Buffer::Data(args[0]); // <------------ Get a backing store from a given argument.
  data += offset;

  std::unique_ptr<RandomBytesRequest> req(
      new RandomBytesRequest(env,
                             obj, …