Google NaCl "Native Client" with Go Lang

Go Lang "Playground" (also used in Tour of Go) is reporting "OS" as NaCl.
Go 1.3 Release Notes - The Go Programming Language
Inside the Go Playground - The Go Blog

NaCl: "Native Client" is a Google tool developed
for safely running x86 code from Chrome web browser
and apparently can be used as a Virtual Machine of a kind.

Welcome to Native Client - Google Chrome:

• Native Client is a sandbox for running compiled C and C++ code in the browser efficiently and securely, independent of the user’s operating system. 
• Portable Native Client extends that technology with architecture independence, letting developers compile their code once to run in any website and on any architecture.