Diversity-conscious admissions/hiring is essentially about trying to compensate for past disadvantages. Gender and race are used as proxies, but they're obviously lacking in many ways (the woman's parents could have both been engineers, she could have been surrounded by pro-STEM culture, the native pacific islander could be a millionaire, he could have been to the most expensive private schools in existence) - so I think the right thing to do would be to detach disadvantage estimation from narrow self-reporting and base it on credible signs of disadvantage, like growing up in a neighborhood with a lot of crime.

That's probably never going to happen, though - anything that cut across the real lines of advantage and disadvantage would mean the Google executives establishing the policy would be hurting their own kids the most.