message: Remove the Shadow DOM from the Tab widget. It wasn't being used anyway.
diff: @@ -7,8 +7,6 @@ import * as DomUtils from '../DomUtils';
  import * as Util from './Util';
  import Logger from '../Logger';
  -const ID = "EtTabTemplate";
  -
  let registered = false;
  /**
  @@ -63,9 +61,6 @@ export class Tab extends HTMLElement {
  */
  createdCallback() {
  this._initProperties();
  - const shadow = this.attachShadow({ mode: 'open', delegatesFocus: false });
  - const clone = this.createClone();
  - shadow.appendChild(clone);
  this._mutationObserver = new MutationObserver( (mutations) => {
  this._applyDraggable();
  @@ -73,17 +68,6 @@ export class Tab extends HTMLElement {
  this._mutationObserver.observe(this, { childList: true });
  }
  - private createClone() {
  - let template = <HTMLTemplateElement>window.document.getElementById(ID);
  - if (template === null) {
  - template = <HTMLTemplateElement>window.document.createElement('template');
  - template.id = ID;
  - template.innerHTML = `<div><slot></slot></div>`;
  - window.document.body.appendChild(template);
  - }
  -
  - return window.document.importNode(template.content, true);
  - }
  attachedCallback(): void {
  this._applyDraggable();
  