[comex]

"Use Native Client. You'll get as close to machine code as you'll ever get, while running in a sandbox. The only way to go faster is to fully trust the code on your machine."

Nitpick: The only way to go faster is to use the hardware privilege separation that Chrome is always already running under, which is considered insufficient to sandbox untrusted code for historical reasons and organizational reasons (Chrome doesn't have much control over the kernels it's running under), but no technical reasons.