Duplicate properties in object literal should be allowed

[zhurvla]

The following should work in > ES6 mode, and throw a SyntaxError: Property "foo" already defined in this object literal. in pre-es6 mode:

(function() {
'use strict';
o = {foo: 1, foo: 2};
o.foo
})();

[rbri]

LGTM but i like to vote for two more tests testing this once for ES6 and once for below. I think this will make our live easier in the long run

[zhurvla]

@rbri Tests added

[rbri]

Thanks a lot!