This error message...
ERROR:nacl_helper_linux.cc(308)] NaCl helper process running without a sandbox!
...implies that the setuid of the sandbox in your system is not configured, hence the program was unable to initiate/spawn a new Browsing Context i.e. Chrome Browser session.
Solution
A quick solution will be, if you want to run Chrome and only use the namespace sandbox, you can set the flag:
--disable-setuid-sandbox
This flag will disable the setuid sandbox (Linux only). But if you do so on a host without appropriate kernel support for the namespace sandbox, Chrome will not spin up. As an alternative you can also use the flag:
--no-sandbox
This flag will disable the sandbox for all process types that are normally sandboxed.
Example:
chromeOptions: {
args: ['--disable-setuid-sandbox', '--no-sandbox']
},