Google always had the ability to use Rust in any of its projects. However, I think Mozilla pissed away the biggest opportunity they had in a decade to lead something that will change an industry, and to influence (positively) the community around it. I certainly trust Mozilla over Google, though I'm still mad about that Mr. Robot extension.
Google has all the resources and hundreds of engineers to throw at Rust. They will definitely have undue influence on the language and its community now that it's in Chrome. I just hope it doesn't wind up looking like Kotlin.
How does being the guardian behind the language help Mozilla in any way?