ActionScript is only supported through the Flash plugin, and inside the Flash environment -- and even that is taken out altogether in the new Chrome release.
C++, not at all. Except if you mean Chrome is written in C++ itself, or you can use Native Client, which again is another plugin like environment.
So, nothing similar to JS at all.
Might as well have mentioned emscripten, which does end up running as a web page.
Because that's the only actual and in use browser I can think of that supports a language other than JS natively.