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 (pageView.pdfPage) {
      return Promise.resolve(pageView.pdfPage);
    }
    if (this._pagesRequests.has(pageView)) {
      return this._pagesRequests.get(pageView);
    }
    const promise = this.pdfDocument
      .getPage(pageView.id)
      .then(pdfPage => {
        if (!pageView.pdfPage) {
          pageView.setPdfPage(pdfPage);
        }
        this._pagesRequests.delete(pageView);
        return pdfPage;
      })
      .catch(reason => {
        console.error("Unable to get page for page view", reason);
        
        this._pagesRequests.delete(pageView);
      });
    this._pagesRequests.set(pageView, promise);
    return promise;
  }
  forceRendering(currentlyVisiblePages) {