if you want a really old example, pnacl. If you want a slightly recent one, FLoC. Not saying those are the best examples, they are just what comes to my head first. I don't really keep up super closely.
pnacl was an example of Google throwing away their homebrewed solution in favour of a common standard (Web Assembly). That seems like a strong argument that they don't push proprietary extensions.
it was an example of them pushing proprietary extensions and eventually removing them again. If I start beating you and then eventually someone calms down and I stop, it's not an example of me not beating you
