title: how to access an asset_path with a digest in a Rails initializer
body: <p>I'm trying to figure out how to use asset_path in a Rails initializer in Rails 4.  I generally use the <code>helpers</code> instance on ActionController::Base to get access to url helpers outside of a view.  However, if you just call <code>asset_path</code> in the initializer it does not append the digest.  For example, this:</p>
  
  <pre><code>puts ActionController::Base.helpers.asset_path("my-image.png")
  </code></pre>
  
  <p>just outputs <code>my-image.png</code>.</p>
  
  <p>The best I could come up with was this:</p>
  
  <pre><code>ActiveSupport.on_load(:after_initialize) do
      puts ActionController::Base.helpers.asset_path('my-image')
  end
  </code></pre>
  
  <p>This works because the after_initialize hook happens after sprockets-rails loads the asset digest helpers into rails.  Is there a way to do this without waiting until after initialization?</p>