This property getter must be called with the PerformanceResourceTiming object as the receiver.
PerformanceResourceTiming
新增于: v18.2.0, v16.17.0
表示从 fetch（HTTP 或缓存）接收的有效负载主体大小（以字节为单位）的数字，单位是在去除任何应用的内容编码之前。
【A number representing the size (in octets) received from the fetch (HTTP or cache), of the payload body, before removing any applied content-codings.】