title: textContent empty in connectedCallback() of a custom HTMLElement
body: <p>Within the <code>connectedCallback()</code> method of my custom element the <code>textContent</code> is returned as an empty string.</p>
  
  <p>Essentially my code boils down to the following...</p>
  
  <pre><code>class MyComponent extends HTMLElement{
      constructor() {
          super()
  
          console.log(this.textContent) // not available here, but understandable
      }           
  
      connectedCallback() {
          super.connectedCallback() // makes no difference if present or not
  
          console.log(this.textContent) // not available here either, but why?!
      }
  }
  
  customElements.define('my-component', MyComponent);     
  </code></pre>
  
  <p>And the HTML...</p>
  
  <pre><code>&lt;my-component&gt;This is the content I need to access&lt;/my-component&gt;
  </code></pre>
  
  <p>From reading about <code>connectedCallback()</code> it sounds like it's called once the element has been added to the DOM so I would expect that the textContent property should be valid.</p>
  
  <p>I'm using Chrome 63 if it helps...</p>