It's almost certain that it is a legal violation and if a lawsuit was brought, I'd bet a million dollars in favour of Google; however, the tool itself isn't the

It's almost certain that it is a legal violation and if a lawsuit was brought, I'd bet a million dollars in favour of Google; however, the tool itself isn't the final product and it's silly, counterproductive and just outright malicious to sabotage efforts at building good tooling in a competitor's company. Plus, it will set precedent and Google would have to vet every single new internal tool against what the previous employers of their employees were doing.