title: Three.js StereoEffect cannot be applied to CSS3DRenderer
body: <p>I'm in the process of developing a chrome VR web app. Now I'm desperately trying to figure out how to render a website into my into my stereoscopic scene which has some meshes in it. </p>
  
  <p>So I have my renderer for the meshes, which works well. The following code is only the relevant snippets:</p>
  
  <pre><code>var renderer = new THREE.WebGLRenderer();
  </code></pre>
  
  <p>Then i have my stereoeffect renderer which receives the webgl renderer:</p>
  
  <pre><code>var effect = new THREE.StereoEffect(renderer);
  </code></pre>
  
  <p>Next is that I create the website renderer, and apply it to the stereoeffect:</p>
  
  <pre><code>var rendererCSS = new THREE.CSS3DRenderer();
  var effectHUD = new THREE.StereoEffect(rendererCSS);
  </code></pre>
  
  <p>Then I have scenes which are being rendered:</p>
  
  <pre><code>var scene = new THREE.Scene();
  var sceneCSS = new THREE.Scene();
  function render(dt) {
        effect.render(scene, camera);
        effectHUD.render( sceneCSS, camera );
      }
  </code></pre>
  
  <p>No what I receive is this: 
  <a href="https://i.stack.imgur.com/i09X2.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/i09X2.jpg" alt="rendered image"></a></p>
  
  <p>A stereoscopic image of my mesh, but a non stereoscopic image of the website. The problem is that the when I try to add the css renderer into the StereoEffect renderer, the setViewport function (among others, probably) are missing. <br>
  I've tried adding the website object to the webgl renderer, but it doesn't want to render my website, so adding the website object to the scene with the meshes doesn't work. <br></p>
  
  <p>Any help is greatly appreciated!</p>