Reportedly the main reason that Google created Chrome originally was to be able to collect detailed data on user behavior. Unlike Analytics, Chrome can provide user metrics on any website that Chromes users ever visit, which clearly includes all the websites that get much traffic at all.. It's true that for obscure sites that don't get much traffic, it could take a while to collect a usable sample. But for websites that get significant traffic, which are the sites that really matter for most searches, Chrome can collect a usable sample in a short time. Google would be crazy to ignore such a gold mine of data. As I said, reportedly the main reason they created Chrome in the first place was to be able to collect such data
Someone mentioned the possibility of artificial manipulation. Actually, Chrome data would be much harder to manipulate than the well-known factors that SEOs have been manipulating for years. The only exception might be sites that hardly get any traffic at all, but they will be mostly left out anyway.
I agree that there could be small biases in the data. But I doubt if they're anywhere near as bad as some of the other biases that already influence the SERPs. For example, websites that express minority views on controlversial social and political issues obviously won't attract as many backlinks as sites that represent majority opinion, and therefore will be unfairly demoted by the algorithm.
So to sum up, If Google isn't using user metrics data as part of their rankings process, they're making a sad mistake, and they will eventually be overtaken and then left behind by a search company that does.