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)

workerId,
            worker.port
          );
          messageHandler.postMessageTransfers = worker.postMessageTransfers;
          const transport = new WorkerTransport(
            messageHandler,
            task,
            networkStream,
            params
          );
          task._transport = transport;
          messageHandler.send("Ready", null);
        }
      );
    })
    .catch(task._capability.reject);
  return task;
}
/**
 * Starts fetching of specified PDF document/data.
 *
 * @param {PDFWorker} worker
 * @param {Object} source
 * @param {PDFDataRangeTransport} pdfDataRangeTransport
 * @param {string} docId - Unique document ID, used in `MessageHandler`.
 * @returns {Promise} A promise that is resolved when the worker ID of the
 *   `MessageHandler` is known.
 * @private
 */
function _fetchDocument(worker, source, pdfDataRangeTransport, docId) {