Improve the performance of performance.

[zhangenming]

function test(f) {
    console.time()
    let i = 0
    while (i++ < 1e6) {
        f()
    }
    console.timeEnd()
}
test(performance.now.bind(performance))
test(()=>performance.now())

// VM2470:7 default: 120.751220703125 ms
// VM2470:7 default: 453.26416015625 ms```

[zhmushan]

[zhmushan]

Can you explain why it is so fast? I've come to the exact opposite conclusion in Nodejs than in the browser. I'm worried that as browsers upgrade, the optimizations we're doing now won't make sense or will even be a hindrance.

[zhangenming]

Can you explain why it is so fast?

const foo = performance.now;
const bar = ()=>performance.now();

// foo() is fast than bar()
// Because less one(1 VS 2) property access need to find, and use `bind` just for fix `this`

I've come to the exact opposite conclusion in Nodejs than in the browser.

I'm not sure, but as far as I know, node's performance seems to be a bit special,
try console.log(performance.now.toString()) in node maybe find something
but I forget the details.

discuss welcome
tested with chrome/firefox/safari, In line with expectations
I don't know if this line of code in vue is in hot path
If not may not have too much necessity of this PR

[zhmushan]

LGTM

[yyx990803]

We already cache getNow() done in the same tick so this likely won't make noticeable difference, but making it faster shouldn't hurt.