chromium looks for plugins in /usr/lib/nsbrowser/plugins. However, on multilib systems it shall be /usr/lib64/nsbrowser/plugins.
+ 14 Jul 2013; Mike Gilbert <floppym@gentoo.org> chromium-28.0.1500.89.ebuild, + chromium-29.0.1547.15.ebuild, chromium-9999-r1.ebuild: + Fix multilib path for plugins, bug 476778.