Method getTransferLayer_

src/service/fixed-layer.js:835–843

* @return {?TransferLayerDef}

()

   * @return {?TransferLayerDef}
   */
  getTransferLayer_() {
    // This mode is only allowed for a single-doc case.
    if (!this.transfer_ || this.transferLayer_) {
      return this.transferLayer_;
    }
    const doc = this.ampdoc.win.document;
    this.transferLayer_ = new TransferLayerBody(doc, this.vsync_);
    return this.transferLayer_;
  }

  /**
   * Find all `position:fixed` and `position:sticky` elements.