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)

const { messageHandler, loadingTask } = this;
    messageHandler.on("GetReader", (data, sink) => {
      assert(
        this._networkStream,
        "GetReader - no `IPDFStream` instance available."
      );
      this._fullReader = this._networkStream.getFullReader();
      this._fullReader.onProgress = evt => {
        this._lastProgress = {
          loaded: evt.loaded,
          total: evt.total,
        };
      };
      sink.onPull = () => {
        this._fullReader
          .read()
          .then(function ({ value, done }) {
            if (done) {
              sink.close();
              return;
            }
            assert(
              isArrayBuffer(value),
              "GetReader - expected an ArrayBuffer."
            );