In the past, some Opera employees do have commit access to Blink. When I was working on the content layer of Chromium (and some other parts) as an Opera employe

In the past, some Opera employees do have commit access to Blink. When I was working on the content layer of Chromium (and some other parts) as an Opera employee I never had commit access, though I do get bug editing access (which is for triaging bugs). Overall, it doesn't feel like there is a community at all, it's more like Google deciding everything then tell external contributors as a courtesy. I believe there can be technical influences driven by non-Google contributors but that's pretty rare. That said, perhaps Microsoft can be an exception if their participation is big enough.