message: Convert Tab widget to the Custom Elements v1 API
diff: @@ -28,7 +28,7 @@ export class Tab extends HTMLElement {
  */
  static init(): void {
  if (registered === false) {
  - window.document.registerElement(Tab.TAG_NAME, {prototype: Tab.prototype});
  + window.customElements.define(Tab.TAG_NAME.toLowerCase(), Tab);
  registered = true;
  }
  }
  @@ -59,7 +59,8 @@ export class Tab extends HTMLElement {
  /**
  * Custom Element 'created' life cycle hook.
  */
  - createdCallback() {
  + constructor() {
  + super();
  this._initProperties();
  this._mutationObserver = new MutationObserver( (mutations) => {
  @@ -69,7 +70,7 @@ export class Tab extends HTMLElement {
  }
  - attachedCallback(): void {
  + connectedCallback(): void {
  this._applyDraggable();
  }
  