Not just Chinese ISPs. I've had Cox inject HTML/Javascript into my HTTP streams for a "test of their emergency messages system" and once for a customer survey.
The survey might have been a DNS redirect instead as by the time I noticed I had already navigated away from the original page and that was one of my few machines that can sometimes use my ISP's DNS.
The emergency message test was HTML/Javascript directly injected into a random non-encrypted page I had loaded.
Mediacom (cable internet in Iowa) does something similar. They insert a banner on the top of every HTTP page you view telling you when you're about to go over your 350GB data cap. Will appear until you click a button to dismiss it.
(Scanning the data is done on government level so I won't even bother to mention it)