Earlier quoted context omitted.
Market share is measured in some very, very funny ways. Like Office 365 being part of their cloud division, including when people download and install office on their computer. If Google was to switch things around, and have Ad-words, Gmail, maps, etc, all pay a small, internal fee to google cloud to host their servers own internal servers, I think the market-share conversation would be very, very different.
Most of internal Google services don't run on Google cloud. Was true as of a couple of years ago and I haven't heard differently from my Google friends recently.
FWIW... most of Amazon's internal infrastructure was NOT run on AWS as of a couple of years ago. The idea that AWS was built to support Amazon is a myth. In fact, most of their own IaaS was a very traditional data center built on converged infrastructure. This is why Amazon was up and running when AWS would have a large outage.