Open brave payments contrib pdf in PDF.js after generated (WIP)

[willy-b]

part of issue #6039

opening this as WIP because it depends on PDF.js being able to open local files (#2714 , I think, but may have been fixed in #6330)

I'm looking into PDF.js myself right now but I am at total newbie with Chrome extensions so feel free to let me know if you have tips on how to fix it.

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests). (not yet)
• Ran git rebase -i to squash commits (if needed). (not squashed yet)

Test Plan:

• Navigate to about:preferences#payments
• Click 'View Payment History'
• Click one of the receipt ilnks
• Choose path to save PDF
• Observe PDF is also opened in new tab

[srirambv]

@willy-b Clicking the link doesn't offer to save the pdf nor retain the pdf opened in new tab. This is on 0.13.0 Preview 7 on Windows 10 x64

[willy-b]

@srirambv yes, contribution PDF feature is still broken on all operating systems following Chromium54 upgrade (see reopen #4769) as the Muon API webview.printToPDF fix from @bbondy (#6450) has not made it into browser-laptop yet.

[willy-b]

since the underlying feature is broken right now by Chromium54 upgrade I am going to cancel this PR, thanks

[willy-b]

@srirambv, I was wrong:
@bbondy's fix actually came into brave/browser-laptop with the Preview7 tag, and I can confirm the underlying feature is working on Linux there, so your observation above was a very useful one. Thanks.

[bbondy]

Ya, I don't think I had it in on all platforms but I think mac and linux probably got it.