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In practice Chrome is not that cross platform. WebGL is an example: Chrome renders differently due to its use of ANGLE, has bad performance due to its GPU blacklist, etc. If you want to support Windows you have to test on Windows, period, regardless of browser.
More generally this take was good back when IE was dominant. Now it's just terrible: Edge is resisting the monoculture, not propagating it. Chrome is working hard to make the OS irrelevant by defeating platform conventions. Standard Mac UI idioms like Quit and Hide don't even work properly in the latest Chrome. Eventually the platforms will become an undifferentiated soup with GMail key equivalents and innovation in OSes will end; why even bother to have more than one OS if it's just to run Chrome?