At the beginning of the build I see error message about missing USER_NS, but compilation continue after that. Because of that I wasted dozens of hours for dead-end compilation.
I believe this is an issue at runtime, so you could just fix your kernel and run Chromium afterwards?
Yes I already fix my kernel, building Chromium right now. But maybe we need to stop compilation when USER_NS is missing?
You don't need to enable USER_NS to build chromium, only to run it. There would be no point in stopping the build.