Get notified when the document finishes loading

[mgodbole]

Hi @paodb
I am using the PDFViewer to load a PDF document from a remote server, using the following

StreamResource resource = new StreamResource("Some file name", () -> {
            try {
                return new URI(PDF_URL).toURL().openStream();
            } catch (Exception e) {
                LOGGER.error(e.getLocalizedMessage(), e);
                return null;
            }
        });

        PdfViewer pdfViewer = new PdfViewer();
        pdfViewer.setSrc(resource);
        pdfViewer.setSizeFull();
        add(pdfViewer);

If the document is large in size, I noticed the UI just shows up blank, waiting for the document to load.
To improve usability, I would like to show an indeterminate ProgressBar.
Is there any way to find out when the loading has finished? I couldn't find any reliable method in the PDFViewer or StreamResource.

Thank you.