If we display recommendations when users save an article, we can help users discover content and acquire more unique users.

SPEC: https://docs.google.com/document/d/1TNavHbgW52yQfgSA3IZtBOZMujX8r0uzliS0SR2w5mA/edit

To run the tests, run this command: ./mach test browser/components/pocket/test/unit/

To test the functionality, it's a bit tricky because nothing happens with it yet, but you can verify it with a breakpoint.

1. Set extensions.pocket.onSaveRecs to true
2. Restart.
3. Ensure you can see the multi process debugger.
4. Log into a Pocket account.
5. Open up a Pocket story. Ideally on that is known to Pocket already, I use stories on newtab.
6. We're going to add a breakpoint to pocket/main.js, but because it's loaded lazily, you need to trigger a save once to enable it, so we can find it, and add the breakpoint. So save a story now.
7. Now in the multi process browser toolbox, look for and open the debugger tab.
8. In the sources window on the left, open Main Thread > chrome:// > content > main.js
9. Go to line 277, and add a breakpoint.
10. Trigger another save on that article.

Expected: it should hit the breakpoint you just set. The data you want to inspect should be in data.recommendations, it is an array, and should have 3 items.

https://hg.mozilla.org/mozilla-central/rev/858282dd490f

https://hg.mozilla.org/mozilla-central/rev/a89fc9a55c2d