extra tests for `Map`, see data-es6.js

Sorry, the compatibility data i have is only for Chrome, Firefox, IE 11.

This test, as written, fails if the browser supports it but doesn't also support Map#forEach. I believe it should instead be written as:
`var map = new Map();
map.set(-0, -0);
return map.has(0) && 1 / map.get(0) === Infinity;`