static getVRDisplay() {
    return new Promise((resolve, reject) => {
      if (!navigator || !navigator.getVRDisplays) {
        let e = new Error('Browser not supporting WebVR');
        e.name = 'WEBVR_UNSUPPORTED';
        reject(e);
        return;
      }

      const rejectNoDisplay = ()=> {
        // No displays are found.
        let e = new Error('No displays found');
        e.name = 'NO_DISPLAYS';
        reject(e);
      };

      navigator.getVRDisplays().then(
        function(displays) {
          // Promise succeeds, but check if there are any displays actually.
          for (let i = 0; i < displays.length; i++) {
            if (displays[i].capabilities.canPresent) {
              resolve(displays[i]);
              break;
            }
          }

          rejectNoDisplay();
        },
        rejectNoDisplay);
    });
  }
returns promise returning list of available VR displays.
@return {Promise<VRDisplay>}