Depends on definition of "possible". There is space, physically. But getting all the paperwork, lining up the money, placating all the NIMBYs and the special interests and politicians may be non-trivial. For Google it may be easier than for other developers, and Google may be more motivated to do it, since galloping housing prices means more salary expenses from Google.
> The people living there don't want that, though, so the laws prohibit it.
In San Jose, there are many multi-tenant developments. Prices are still crazy (compared to any other place outside Silicon Valley).
And there's also a question of infrastructure. Did you ever drive on 101, 85, 87 or 280 in traffic hours? Did you ever drive on adjacent connecting streets? Now imagine there's 3x or 5x people living in the same space. You'd have to start you commute previous day to get to the office by the morning.