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)

* @param {DocumentInitParameters} params - The document initialization
 *   parameters. The "url" key is always present.
 * @returns {Promise} A promise, which is resolved with an instance of
 *   {IPDFStream}.
 * @ignore
 */
/**
 * @type IPDFStreamFactory
 * @private
 */
let createPDFNetworkStream;
/**
 * Sets the function that instantiates an {IPDFStream} as an alternative PDF
 * data transport.
 *
 * @param {IPDFStreamFactory} pdfNetworkStreamFactory - The factory function
 *   that takes document initialization parameters (including a "url") and
 *   returns a promise which is resolved with an instance of {IPDFStream}.
 * @ignore
 */
function setPDFNetworkStreamFactory(pdfNetworkStreamFactory) {
  createPDFNetworkStream = pdfNetworkStreamFactory;
}
/**
 * @typedef { Int8Array | Uint8Array | Uint8ClampedArray |
 *            Int16Array | Uint16Array |
 *            Int32Array | Uint32Array | Float32Array |
 *            Float64Array
 * } TypedArray
 */