https://github.com/discourse/discourse/commit/ebb5c1ff4dddb03c3684adc60fb87b0ee95f4f6a
Whoever thought to include the theme ID in the deprecation notice is brilliant! (And it’s amazing how things like that can take so long to become “obvious”.) Maybe it was @david, at least he committed it.
(No offense intended to the theme in question…)
This saves me on the order of an hour figuring out where to look. (Perhaps a slight exaggeration.)
So fantastic.
Yup! I must have spent so many hours over the last few years manually digging through backtraces to identify problem theme/plugins… and then it dawned on me that we can have a robot do it!! 
None taken. 
Btw, I’ve pushed a commit replacing this.container by this.register to get rid of the warning. @pfaffman can you try and confirm that it is gone?
Awesome! That did it. I was going to try to submit a PR yesterday but got in a fight with git.
Thanks!