Remember, Chrome is partly so popular because it's so blazingly fast, even on very non-impressive hardware.
Even today, here in 2012, with all the mighty hardware we have, and even with the very latest cutting-edge safe managed no-sharp-edges languages and tools mankind has yet invented, C/C++ still can offer such an overwhelming improvement as to be worth it.
Especially when you consider just how few exploits Chrome has had, and how incredibly complex this one was to pull off. Clearly, C++ can be used to write highly secure software just fine, thank you.
Whatever theoretical academic super-secure language you're thinking of as a C++ replacement, at this point I'd be willing to bet that there's more exploitable holes in that language's compiler/VM/runtime than there are in Chrome's C++ codebase. :)