This patch contains the following improvements:
- Only fetch the various document properties *once* per PDF file opened, and cache the result (in a frozen object).
- Always update the *entire* dialog at once, to prevent inconsistent UI state (issue 8371).
- Ensure that the dialog, and all its internal properties, are reset when `PDFViewerApplication.close` is called.
- Inline, and re-factor, the `getProperties` method in `open`, since that's the only call-site.
- Always overwrite the fileSize with the value obtained from `pdfDocument.getDownloadInfo`, to ensure that it's correct.
- ES6-ify the code that's touched in this patch.
Fixes 8371.
Note that as discussed on IRC, this makes the viewer slightly slower to load *only* in `gulp server` mode, however the difference seem slight enough that I think it will be fine.
The sidebar code has, except for minor fixes/additions (such as attachments), been largely untouch for years.
To avoid having a bunch of sidebar code sprinkled throughout viewer.js, this patch moves the sidebar code into a separate file (pdf_sidebar.js), similar to how most other functionality has been moved in the last few years.
Besides simply moving code around, this patch also has the added benefit that we now keep track of the sidebar state (not just opened/closed).
This now makes it possible to handle both `Preferences` *and* `ViewHistory` settings for the sidebar state in a cleaner way, preventing strange and confusing interactions between the two.
