Performance：timing 属性
Deprecated
Avoid using this feature in new projects.
This feature is supserseded by the PerformanceNavigationTiming API.
This feature may be a candidate for removal from web standards or browsers.
Consider using the following features instead: Performance或Navigation timing.
遗留的 Performance.timing 只读属性会返回一个与延迟相关的性能信息的 PerformanceTiming 对象。
该属性在 worker 中不可用。
警告：此属性已在 Navigation Timing 第 2 版规范中被弃用。请改用 PerformanceNavigationTiming 接口。