Interesting question.

I would try do diversify more aggressively than Google seems to be doing presently. Even though Google has a excellent grip on the search market, market share in the internet arena has been demonstratedly ephemeral in some cases, so diversifying more aggressively is a hedging strategy. Specifically:

Continue to concentrate on making search better, more useful, faster, etc., as number one priority.

Start two new independent clean-slate next-gen mobile OS efforts, in case they are needed, that are closed, in case that is an important advantage.

Acquire wind turbine generator technology firms

Buy up many transportation efficiency startups, i.e., new electric motors, improved internal combustion motors, new transmission, new battery, system integrators, etc.

Invest in hydraulic hybrid technology; buy patents, startups, etc.

As other have mentioned, leverage the massive amounts of data Google has to advance NLP and related, and try to figure out a way to make money from it

Fund three startups the goal of creating a hybrid drive conversion that would turn an existing car into a hybrid car in a cost effective manner

Fund a few internet education startups, look for opportunities in education area generally.