Simple Array Destructuring shouldn't require use of $jscomp

When using a very simple destructuring pattern, it should be possible to convert this to simple assignments. Reading the spec, http://www.ecma-international.org/ecma-262/6.0/#sec-destructuring-assignment, I can see why the definition of `$jscomp` is what it is, but it seems like overkill for simple assignments.

Given the input:

``` javascript

function add(a) {
let [b,c] = a;
return b+c;
}

add([1,2])
```

I would expect the output to be something along the lines of:

``` javascript
function test(a) {
var b = a[0], c = a[1];
return b+c;
}

test([1,2])
```

Instead, what I'm seeing is:

``` javascript
/* $jscomp definition */;
function add(a){
var b=$jscomp.makeIterator(a);
a=b.next().value;
b=b.next().value;
return a+b
}
add([1,2]);
```