connectRoot(root) {
    this.roots.add(root);

    if (this.observer) {
      this.observer.observeRoot(root);
    }
  }
Add `root` to the list of roots managed by this `DOMLocalization`.

Additionally, if this `DOMLocalization` has an observer, start observing
`root` in order to translate mutations in it.

@param {Element}      root - Root to observe.