"it depends"

Some bits are self explanatory (sales, marketing, ...). Chances are most of the "brains" of Google (coders and the like) fall under R&D since that is often taxed more favourably. A lot of staff, particularly the people who literally keep the lights on (anyone who works on data centre hardware) will fall under cost of revenue.

For those of us who are not seasoned accountants:

• Research and Development
• Sales and Marketing
• General and Administrative