You can ask your users to install the gem from git (bundler: http://bundler.io/git.html, Install Gem from Github Branch?).
This will result in a line like
gem 'hard_drive_expander', github: 'rodrigo/hard_drive_expander'
in a Gemfile (or a bit a lengthier process for gem install
- do you intend 'library' kind of usage or standalone installations). Note that depending on your scenario you could have an installer gem that depends on the "github-hosted" gem, or downloads and builds/installs it (both seem like dirty solutions to me though, its not what I expect or commonly see).
Although github does place quotas on your repositories, you will probably not hit them (https://help.github.com/articles/what-is-my-disk-quota/).
Another option is to host it yourself (http://guides.rubygems.org/run-your-own-gem-server/).
Sorry for the "linky" answer.
However, @icguida and @engineersmnky s comments to your question are very worth considering: Do you really need to include chromium?
Update
There is a gem that will hook into gem
to allow for usage like this: gem specific_install https://github.com/githubsvnclone/rdoc.git
. The gem is called specific_install: https://github.com/rdp/specific_install .