Fix webcomponents.js.d.ts and test

webcomponents.js/webcomponents.js-tests.ts

@@ -15,6 +15,8 @@ var XFoo = document.registerElement("x-foo", {
 });
 
 var xFoo = new XFoo();
+xFoo.textContent = "";
+document.body.appendChild(xFoo);
 
 window.CustomElements.hasNative;
 window.CustomElements.flags;

webcomponents.js/webcomponents.js.d.ts

@@ -11,7 +11,7 @@ declare module webcomponents {
     }
 
     export interface CustomElementConstructor {
-        new():HTMLElement;
+        new(): HTMLElement;
     }
 
     export interface CustomElementsPolyfill {