There's a few things that could be improved in the current implementation, such as:
- It's currently necessary to *both* manually track the `featureId`s which should trigger delayed fallback, as well as manually report telemetry in affected cases.
Obviously there's only two call-sites as of now (forms and javaScript), but it still feels somewhat error-prone especially if more cases were to be added in the future. To address this, this patch adds a new (private) method which abstracts away these details from the call-sites.
- Generally, it also seems nice to reduce *and* simplify the amount of state we need to store on `PDFViewerApplication` in order to support the "delayedFallback" functionality.
Also, having to *manually* work with the "delayedFallback"-array in multiple places feels cumbersome and makes e.g. the `PDFViewerApplication.fallback` method less clear as to its behaviour.
- Having code *outside* of `PDFViewerApplication`, i.e. in the event handlers, directly access properties which are marked as "private" via a leading underscore doesn't seem that great in general.
Furthermore, having the event handlers directly deal with that should be internal state also seem unfortunate. To address this, the patch will instead make use of a new `PDFViewerApplication.triggerDelayedFallback` callback.
- There's at least one code-path in the viewer, see `PDFViewerApplication.error`, where `fallback` can be called without an argument.
It's currently possible (although maybe somewhat unlikely) that such a call *could* be overridden by the `featureId` of a pending "delayedFallback" call, thus not reporting the *correct* fallback reason.
- The "delayedFallback"-state weren't being reset on document close (which shouldn't affect Firefox, but nonetheless it ought to be fixed).
625f8a6f51