   var vrPresentButton = null;

      // ================================
      // WebVR-specific code begins here.
      // ================================

      // WebGL setup.
      var webglCanvas = document.getElementById("webgl-canvas");
      var gl = null;
      var cubeSea = null;
      var stats = null;

      function initWebGL (preserveDrawingBuffer) {
        // Setting preserveDrawingBuffer to true prevents the canvas from being
        // implicitly cleared when calling submitFrame or compo