application.js

goog.require('goog.dom');

function sayHi() {
  var newHeader = goog.dom.createDom('h1', {'style': 'background-color:#EEE'}, 'Hello world!');
  goog.dom.appendChild(document.body, newHeader);
}

closure.rb

# initializer

require 'klosure-tilt'

path = File.expand_path("../../../app/assets/javascripts/closure-library/closure", __FILE__)
p [:closure_lib_path, path]

Rails.application.assets.append_path path
Rails.application.assets.register_preprocessor 'application/javascript', ClosureDependenciesProcessor

klosure-tilt.rb

require 'tilt'

class ClosureDependenciesProcessor < Tilt::Template
  def prepare; end

  def evaluate(context, locals, &block)
    p [:CALCDEPS_START]
    p [:data, data]

    context.require_asset 'goog/base'

    data.lines.each do |line|
      if line =~ /goog\.require\s*\(\s*[\'\"]([^\)]+)[\'\"]\s*\)/
        goog, mod, sub = $1.split(".")
        sub ||= mod
        mod, sub = mod.downcase, sub.downcase
        dep = [goog, mod, sub].join("/")

        p [:require_asset, dep]
        context.require_asset(dep)
      end
    end

    data
  end
end