Show an error when this used before super

[saschanaz]

I'm not 100% sure this is by ES6 spec but the following code errors on Edge and Firefox Nightly:

new (class extends Promise {
  constructor() {
    let newThis = this; // Edge: Use before declaration, Firefox: |this| used uninitialized in anonymous class constructor
    super((resolve, reject) => resolve());
  }
})()

[vladima]

duplicate of #4211