Support v1 Custom Element syntax

[Bruce Anderson]

Are there plans to add an adapter (or something), so that one can define a polymer component using as much of the V1 custom spec as possible?  Something like:

<dom-module id="flag-icon">
  <template>
   <div>Country Code: [[CountryCode]]</div>
</template>
</dom>

<script>

class FlagIcon extends HTMLElement {
  constructor() {
    super();
    this._countryCode = null;
  }

  static get observedAttributes() { return ["country"]; }

  attributeChangedCallback(name, oldValue, newValue) {
    // name will always be "country" due to observedAttributes
    this._countryCode = newValue;
    this._updateRendering();
  }
  connectedCallback() {
    this._updateRendering();
  }

  get country() {
    return this._countryCode;
  }
  set country(v) {
    this.setAttribute("country", v);
  }
}

Polymer.registerV1CustomElement(FlagIcon)

</script>