Fix chrome process lifetime

[gitlabmike]

Fix chrome process lifetime by trying to nicely terminate the process before killing. Also wait for process to exit before returning from ExitProcess.

This became an issue when trying to get isolation between integration tests. It's a race on the chrome process exiting before we are starting them again.

Note: I wasn't able to get the tests running on my machine so I couldn't verify if any of the tests are impacted.