Plans: Add a/b test with 'upgrade' button in the sidebar

[drewblaisdell]

Fixes #2382.

This adds an a/b test to change the label in the sidebar next to 'Plans' from 'Free' to a button with the label 'Upgrade'.

original variation:

button variation:

I'll update the datestamp for this test before merging to the current day.

Testing
original:

• Run localStorage.setItem( 'ABTests', '{"plansUpgradeButton_20040114":"original"}' ); in the console.
• Visit /stats/year/:site (or any 'My Sites' route) for a site with the free plan.
• Assert that you see the 'Free' label next to 'Plans' in the sidebar.

original:

• Run localStorage.setItem( 'ABTests', '{"plansUpgradeButton_20040114":"button"}' ); in the console.
• Visit /stats/year/:site (or any 'My Sites' route) for a site with the free plan.
• Assert that you see the 'Upgrade' button next to 'Plans' in the sidebar.
• Product review
• Code review

cc @breezyskies

[stephanethomas]

I noted that on my todo list but since you're updating this file could you add more context to this translation? I guess just explaining it's for free trials for plans would really help translators to deliver a more accurate translation.

[stephanethomas]

A quick note that Upgrade might be translated in longer strings in some languages (for example it would be Mettre à jour in French). I know the test will run only for English users but that's something we should probably keep in mind, considering we don't have much room in this sidebar.

[breezyskies]

Tested and works as described. 👍

A quick note that Upgrade might be translated in longer strings in some languages (for example it would be Mettre à jour in French). I know the test will run only for English users but that's something we should probably keep in mind, considering we don't have much room in this sidebar.

Definitely something to keep an eye on. I will note that it does appear to handle this pretty well right now and (while still not being ideal) at least doesn't break the layout:

[drewblaisdell]

Thanks for looking at this, @breezyskies and @stephanethomas. I updated the commit to add context to the 'Trial' translation string and made the logic for using the button a bit more clear.

[stephanethomas]

Code looks good. We're good to go here.