PHP 计算页面执行时间

$t = new executeTime;
//phpinfo();
for($i=0;$i<10;$i++){
echo $i.'<br>';
}

class executeTime{
private $microtime;
public function __construct(){
$this->microtime = microtime(true);
}

public function getNow(){
$this->__dectruct();
}

public function __destruct(){
if (empty($_SERVER['REQUEST_TIME_FLOAT'])){
echo '<div style="color:#fff;background:#000;position:absolute;top:0px;right:0px;padding:3px 6px;">本次执行时间：', microtime(TRUE) - $this->microtime, '秒</div>';
}else{
echo '<div style="color:#fff;background:#000;position:absolute;top:0px;right:0px;padding:3px 6px;">本次执行时间：', microtime(TRUE) - $_SERVER['REQUEST_TIME_FLOAT'], '秒</div>';
}
}
}