I was wondering if WebGL is considered stable enough to be enabled by default. It makes some PDFs render much faster and it has been off by default for a while now, so we have had quite some time to test it.

If we decide to enable WebGL by default, we should not forget to update https://github.com/mozilla/pdf.js/blob/master/extensions/chromium/preferences_schema.json#L39 as well.

/cc @yurydelendik 
/cc @Snuffleupagus (because IIRC you were testing WebGL too)

if (worker.destroyed) {
    return Promise.reject(new Error("Worker was destroyed"));
  }
  if (pdfDataRangeTransport) {
    source.length = pdfDataRangeTransport.length;
    source.initialData = pdfDataRangeTransport.initialData;
    source.progressiveDone = pdfDataRangeTransport.progressiveDone;
    source.contentDispositionFilename =
      pdfDataRangeTransport.contentDispositionFilename;
  }
  return worker.messageHandler
    .sendWithPromise("GetDocRequest", {
      docId,
      apiVersion:
        typeof PDFJSDev !== "undefined" && !PDFJSDev.test("TESTING")
          ? PDFJSDev.eval("BUNDLE_VERSION")
          : null,
      
      source: {
        data: source.data,