Principal engineer at ChangeTip here (https://www.linkedin.com/in/jimlyndon). I actually built the first ever bitcoin tip button for content creators.

The tip payment page (Tip.me) was actually launched on July 29th, 2014. The tip.me (bitcoin tip) button was launched on August 28th, 2014. I've attached what they looked like at that time and you can do an image search or other internet archive research to see that they were indeed active then. (we also have our code repository to back us up on that):

There was a small update (counter for number of tippers) and marketing push that happened in November, as you remember. We released our current version 2 in Jan 2015 (which I also built) that included a new look and feel and better integration with our Wordpress plugin:

Since CoinBase, at least in your abstract above, doesn't actually mention "bitcoin" in their tip button description, you could also look at Flattr's tip buttons, gittip, and I'm sure you could find others.

Cheers!