Split out from Bug #1653607
Implement the picker in the new Print UI to select from the list of available paper sizes for the current printer, and update the print settings when the selection changes.

There's a question about what the paper size picker should show and do if the selected "printer" is our print-to-pdf file destination. There may be a subset of common paper sizes we can support, but this could be region-specific. In the meantime, the plan is to show and use the default settings.paperName and disable the picker.

Adding leave-open as I'd like to land the new string while the rest of the patch is getting worked out.

https://hg.mozilla.org/mozilla-central/rev/1372364729f7

Bug 1659781 is implementing an array of nsIPaper objects for use in the print-to-PDF case where the "printer" doesnt define its own paper list.

Comment on attachment 9171310 [details]
Bug 1659757 - Part 1: Add string for paper-size picker. r?emalysz

Beta/Release Uplift Approval Request

• User impact if declined: We'll need this on Beta to implement the paper size picker, and presumably new l10n strings for Beta should be uplifted as early as possible.
• Is this code covered by automated tests?: No
• Has the fix been verified in Nightly?: Yes
• Needs manual test from QE?: No
• If yes, steps to reproduce:
• List of other uplifts needed: None
• Risk to taking this patch: Low
• Why is the change risky/not risky? (and alternatives if risky): It adds a single string for l10n that is currently unused.
• String changes made/needed: Adding one string "Paper size"

• Build dictionary of paper sizes at init and whenever the printer changes
• Resolve async properties on the selected paper
• Pick a default when the given paper size isn't available
• Add virtual properties for paperSize and defaultPaperName
• Refresh margin settings when the paperName changes as these may be computed

Comment on attachment 9171310 [details]
Bug 1659757 - Part 1: Add string for paper-size picker. r?emalysz

This string landed before soft freeze. The actual paper size implementation is in attachment 9173188 [details], which will need to get uplifted once its reviewed.

https://hg.mozilla.org/mozilla-central/rev/5b22c5ab5a2d

Comment on attachment 9173188 [details]
Bug 1659757 - Add paper size picker. r?mstriemer

Beta/Release Uplift Approval Request

• User impact if declined: User is unable to change paper size when printing in the new print UI.
• Is this code covered by automated tests?: No
• Has the fix been verified in Nightly?: No
• Needs manual test from QE?: Yes
• If yes, steps to reproduce: 1. Open the print dialog

2. Click on "more settings" to reveal the paper size picker

3. Confirm that the dropdown contains appropriate paper sizes for the selected printer

4. Selecting different sizes should update the preview, and result in the output (print or PDF file) using the correct width/height properties

5. Select any printer that isn't the Mozilla print to PDF pseudo-printer from the destination picker

6. Select a common, not-default paper size such as US Letter or A4.

7. Change the selected printer to the Mozilla PDF printer

8. If the PDF printer supports a similar paper size, this should still be selected in the paper size picker

• List of other uplifts needed: None
• Risk to taking this patch: Low
• Why is the change risky/not risky? (and alternatives if risky): Front-end changes to the new Print UI which is behind a pref.
  The string this feature needs was landed before the 82 branching, in https://hg.mozilla.org/mozilla-central/rev/1372364729f7
• String changes made/needed: None

Adding bug 1660527 as blocking this, in case that helps get the stack lined up right on beta.

Comment on attachment 9173188 [details]
Bug 1659757 - Add paper size picker. r?mstriemer

Approved for 81.0b6.

https://hg.mozilla.org/releases/mozilla-beta/rev/9c6a80db1401

Confirming this issue as verified fixed on macOS 10.15, Ubuntu 18.04 and Windows 10x64. Verified using 82.0a1 (2020-09-09) and 81.0b8.