Function onprogress

example/tests/gm_download_test.js:450–454

(p)

    const opts = {
      ...details,
      onprogress(p) {
        progress.push(p);
        try { details.onprogress && details.onprogress(p); } catch {}
        updateProgress(p.loaded ?? p.done ?? 0, p.total ?? p.totalSize ?? -1);
      },
      onload(data) {
        try { details.onload && details.onload(data); } catch {}
        resolve({ kind: saveCancelled ? "save_cancelled" : "load", data });