The built-in PDF Viewer (in Firefox) cannot use the browser findbar when PDF files are embedded in e.g. iframe/object tags, and the PDF.js findbar (i.e. `PDFFindBar`) will thus be used instead in those cases.
This is slightly problematic, since the `MOZCENTRAL` version of the viewer uses a special, slimmed down, version of the `l10n.js` file that doesn't (currently) support plural forms. To prevent the matchesCounter from breaking completely in this edge-case, temporarily hard-code the plural form to use the default `[other]` version of the locale strings.
The property is intended to contain a reference to a DOM element, which not only is nowhere to be found *now* but appears to never have existed in the first place.
As outlined in https://bugzilla.mozilla.org/show_bug.cgi?id=1282759 the internal Firefox name for the feature is `entireWord`, hence that name is used here as well for consistency (with "Whole words" being limited to the UI).
Given existing limitations of the PDF.js search functionality, e.g. the existing problems of searching across "new lines", there's some edge-cases where "Whole words" searching will ignore (valid) results.
However, considering that this is a pre-existing issue related to the way that the find controller joins text-content together, that shouldn't have to block this new feature in my opionion.
*Please note:* In order to enable this feature in the `MOZCENTRAL` version, a small follow-up patch for [PdfjsChromeUtils.jsm](https://hg.mozilla.org/mozilla-central/file/tip/browser/extensions/pdfjs/content/PdfjsChromeUtils.jsm) will be required once this has landed in `mozilla-central`.
For the `PDFFindBar` implementation, similar to the native Firefox findbar, the matches count displayed is now limited to a (hopefully) reasonable value.
*Please note:* In order to enable this feature in the `MOZCENTRAL` version, a follow-up patch will be required once this has landed in `mozilla-central`.
After PR 8394, where the l10n service was converted to be asynchronous, we're no longer calling `_adjustWidth` after updating the `findMsg` label. Hence it's currently possible that the width of the findbar won't be correct. The solution is simple though, just call `_adjustWidth` after the `findMsg` label has been (asynchronously) updated.
Another existing issue, which was an oversight in PR 8132, is that `PDFFindBar.updateResultsCount` may be called directly from `PDFFindController`. In that case, we're not calling `_adjustWidth` at all, which means that the findbar may also not have the correct width.
The simple solution here is to always call `_adjustWidth` at the end of `updateResultsCount` (which is why we no longer need the `_adjustWidth` call at the end of `updateUIState`).
Currently we're *only* hiding the label, but not actually resetting it until a new match is found.
Obviously it's being hidden, but it seems that it really ought to be completely reset as well (since e.g. `PDFFindBar.reset` won't technically reset *all* state otherwise).
Note that these files were among the first to be converted to ES6 classes, so it probably makes sense to do another pass to bring them inline with the most recent ES6 conversions.
Moreover, rename `FindStates` to `FindState` since enumeration names are
usually not in plural, for readability and consistency with the ones in
`src/shared/util.js`.
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.
