static parseVastToInterstitials(vast, currentTime) {
    const TXml = shaka.util.TXml;
    /** @type {!Array<shaka.extern.AdInterstitial>} */
    const interstitials = [];

    for (const ad of TXml.findChildren(vast, 'Ad')) {
      const inline = TXml.findChild(ad, 'InLine');
      if (!inline) {
        continue;
      }
      const creatives = TXml.findChild(inline, 'Creatives');
      if (!creatives) {
        continue;
      }
      for (const creative of TXml.findChildren(creatives, 'Creative')) {
        const linear = TXml.findChild(creative, 'Linear');
        if (linear) {
          shaka.ads.Utils.processLinearAd_(
              interstitials, currentTime, linear);
        }
        const nonLinearAds = TXml.findChild(creative, 'NonLinearAds');
        if (nonLinearAds) {
          const nonLinears = TXml.findChildren(nonLinearAds, 'NonLinear');
          for (const nonLinear of nonLinears) {
            shaka.ads.Utils.processNonLinearAd_(
                interstitials, currentTime, nonLinear);
          }
        }
      }
    }
    return interstitials;
  }
@param {!shaka.extern.xml.Node} vast
@param {?number} currentTime
@return {!Array<shaka.extern.AdInterstitial>}