for-in bytecode generation is exponential

[Saam Barati]

we emit the loop 3 times. If we start nesting for-in loops, this is exponential. I'll verify this is indeed the case.

[Saam Barati]

Yup. We emit 1072675 instruction words for this function:
```
function foo(o) {
    for (let i in o) {
        for (let i in o) {
            for (let i in o) {
                for (let i in o) {
                    for (let i in o) {
                        for (let i in o) {
                            for (let i in o) {
                                for (let i in o) {
                                    for (let i in o) {
                                        2+2;
                                    }
                                }
                            }
                        }
                    }
                }
            }
        }
    }

}
```

[Alexey Shvayka]

Keith is fixing for / in to emit only one loop in https://bugs.webkit.org/show_bug.cgi?id=227989.

*** This bug has been marked as a duplicate of bug 227989 ***