Return a reference to the injected html

In JsTestDriver you could get a reference to the injected html, so you don't need to search for the element in the document:

    /*:DOC foo = <div><p>foo</p></div>*/
    assertNotUndefined(this.foo);

With injectHtml:

    var foo = injectHTML("<div><p>foo</p></div>");
    assertNotUndefined(foo);