If Google wants to start charging for a single product it owns, which would it be and why?

This is an interesting question posted earlier but changed. Not sure why.
 Google has various products available today such as Google Search, Gmail, Maps, Image Search, Android OS, Drive, Calendar.

Clarifying questions:

Why is Google interested in charging money for their free product? Are they not generating revenue from ads in this product?
Is a freemium model allowed? Example: Youtube was free and Youtube Premium has now come
Can I price to B2B customers or B2C customers?
Is it a one-time price or subscription model?
How much profit/revenue is Google expecting from this change? Market Size?

I think there are certain things Google should research before charging for a free product:
1. Google should be a major player with no good alternative and barriers to entry for others should be high enough.
2. Google has determined the right price for the service
3. Google should not lose credibility and goodwill by charging for a service that is free but still earning profit for Google

The product I would go for today is:
Android OS charged to Device manufacturers. The reason for this is

1. There is no good alternative in the world today than Android OS with millions of android apps available. As iOS is only available to Apple phones and still has much lesser apps than Android, there is a huge barrier to entry for others.

2. Device manufacturers will absorb the cost (which will be not very high) in the device price itself. Google can provide customization features available with these pricing plans so that even device manufacturers see value out of this.
 

3. Google does not lose goodwill among the billions of users as they are not directly charged.

 

 The next step is to determine the right price. I would say that seeing that this is a lifetime licence based model and Android OS phones have a life to 2 years, Google should charge this licence in a way that cost does not affect Android buyers too much as the market is huge and they will be benefited with economies of scale. Anything like $10 X 2 billion android users = $20 billion in revenue. (Disclaimer:Pricing has not been done thoroughly in this question by me as it was not the focus)