Running C++ in a browser app? Can't see that one blowing up in anyone's face.
Of course, the big probale is you need a language that can be made to run in a very secure sandbox. Java, python, and related languages could be made to do so with some work. They run on VM's or have an interpreter. But C++? If you're talking about creating a new implementation that runs in an interpreted/virtualized/sandboxed environment and has built-in memory management thrown in, then that might be a possibility. But then again, why would you want to do that when there are so many other ones out there.
"The only way I can lose this election is if I'm caught in bed with a dead girl or a live boy." -- Louisiana governor Edwin Edwards