Seems like the idea here is to ensure that this class is a singleton, which is correct, since we don't want to double-enable xhprof (I wonder what that would cause?), but maybe the solution here is to have something like this:

```php
private function __construct() { ... }
public static function instance() {
  static $instance = null;
  if ($instance === null) {
    $instance = new ProfilerXhprof();
  }
}
```

That way, we can't call new ProfilerXhprof() and end up with an instance that is not the same instance that is profiling data for us.