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)

return; 
          }
          throw readyReason;
        });
      };
    });
    messageHandler.on("GetDoc", ({ pdfInfo }) => {
      this._numPages = pdfInfo.numPages;
      loadingTask._capability.resolve(new PDFDocumentProxy(pdfInfo, this));
    });
    messageHandler.on("DocException", function (ex) {
      let reason;
      switch (ex.name) {
        case "PasswordException":
          reason = new PasswordException(ex.message, ex.code);
          break;
        case "InvalidPDFException":
          reason = new InvalidPDFException(ex.message);
          break;
        case "MissingPDFException":
          reason = new MissingPDFException(ex.message);
          break;
        case "UnexpectedResponseException":
          reason = new UnexpectedResponseException(ex.message, ex.status);
          break;
        case "UnknownErrorException":
          reason = new UnknownErrorException(ex.message, ex.details);
          break;
      }
      if (!(reason instanceof Error)) {