Add some UI feedback when a PDF fails to load for any reason

[Rob--W]

The generic errorWrapper was removed in #15533, motivated by code simplification and reducing the translated strings. The result is zero UI feedback when the PDF fails to load/render for any reason.

Examples:

• Confusion when opening files manually: "Invalid or corrupted PDF file" message is missing, only blank page is shown #16271
• Chrome extension, when the user opens the viewer UI with an invalid destination, e.g. chrome-extension://oemmndcbldboiebfnladdacbdfmadadm/http://example.com/not-a-pdf

I'd like to restore the UI feedback, at least in the Chrome extension. It doesn't have to be the same as the original, even dumping the raw error message (which are still translated by the way) would suffice.

[Rob--W]

@Snuffleupagus As the author of #15533, what do you think of this? Should this be in the generic viewer UI or be Chrome-specific?

[Snuffleupagus]

As the author of #15533, what do you think of this?

That was done specifically to reduce the amount of code that needs to be maintained. Furthermore, the current behaviour is also consistent across builds since the Firefox PDF Viewer no longer displays any error messages (except the console logging).

There's some discussion in https://bugzilla.mozilla.org/show_bug.cgi?id=1795859 about possible surfacing error messages more visibly, hence I very much believe that we should await the conclusion of that bug before re-adding any build-specific code to the viewer for this purpose.

[Rob--W]

Thanks for linking that issue. I'll link this issue from Bugzilla, so that if there is any resolution, it will be mirrored to both issue trackers.

[Rob--W]

@Rob--W how can i explore more about the issue?

If you are wondering about how to trigger this scenario, see #16271 for manual reproduction steps.

Note that this issue is not yet actionable until a decision has been made (see #16599 (comment)).