For browser tests outside of //chrome, we basically have them reuse the content browsertest classes. Specifically, the content API has 
https://source.chromium.org/chromium/chromium/src/+/main:content/public/test/content_browser_test.h.
However, that uses things like 
Shell, which means that just about every non-trivial browsertest has to specially DEPS in //content/shell.
Running this by you folks, but if we want to expose content::ContentBrowserTest in the content API, we should also expose enough of the pieces to let it be fully used without having to bypass the API.
Avi