[ES6] Arrow function syntax. Add missed test for using 'with' and 'this' in arrow function.

[GSkachkov]

Add tests that cover following case in arrow function

function foo() {
    let arr = () => {
        with ({'this': 40}) {
            return this;
        }
    }
    return arr();
}

let o1 = {'this': 20};

assert(o1 === foo.call(o1));

[GSkachkov]

Created attachment 275475 [details]
Patch

[WebKit Commit Bot]

Comment on attachment 275475 [details]
Patch

Clearing flags on attachment: 275475

Committed r198978: <http://trac.webkit.org/changeset/198978>

[WebKit Commit Bot]

All reviewed patches have been landed.  Closing bug.