ERROR at //build/config/linux/gconf/BUILD.gn:9:1: Assertion failed. assert(!is_chromeos && use_gconf) ^----- See //ui/accessibility/BUILD.gn:107:7: which caused the file to be included. "//build/config/linux/gconf", ^---------------------------
I think ui/accessibility/BUILD.gn is missing an "if (use_gconf)" check.
Pushed https://gitweb.gentoo.org/repo/gentoo.git/commit/www-client/chromium?id=2d587c01e3a0b8def67e393e1a9288561aaa94c8 for now. Fixing build files will take more than one "if" - I've tried that and didn't succeed. I may look into this more. Thanks for testing!
This should be fixed now in M54+ (and masked in M53).