static findOrMakeSpecialCanvases_(container, canvases, vrCanvases) {
    let lcevcCanvas = null;
    for (const canvas of canvases) {
      goog.asserts.assert(canvas.tagName.toLowerCase() == 'canvas',
          'Should be a canvas element!');
      if (canvas.parentElement == container) {
        lcevcCanvas = canvas;
        break;
      }
    }
    if (!lcevcCanvas) {
      lcevcCanvas = document.createElement('canvas');
      lcevcCanvas.classList.add('shaka-canvas-container');
      container.appendChild(lcevcCanvas);
    }
    let vrCanvas = null;
    for (const canvas of vrCanvases) {
      goog.asserts.assert(canvas.tagName.toLowerCase() == 'canvas',
          'Should be a canvas element!');
      if (canvas.parentElement == container) {
        vrCanvas = canvas;
        break;
      }
    }
    return {
      lcevcCanvas,
      vrCanvas,
    };
  }
@param {!Element} container
@param {!NodeList<!Element>} canvases
@param {!NodeList<!Element>} vrCanvases
@return {{lcevcCanvas: !Element, vrCanvas: ?Element}}
@private