Introduces a 'supportsDownloading' browser option (defaulting to false)
that lets embedders disable the save/download paths entirely. When
disabled:
- the toolbar and secondary-toolbar download buttons are hidden;
- PDFViewerApplication.{download,save,downloadOrSave} and the
"beforeunload" save prompt bail out early;
- the BaseDownloadManager helpers (download, downloadData,
openOrDownloadData) and the Firefox/generic _triggerDownload
implementations no-op.
ece1e2ed0c