thin wrapper around Hash that allows us to lazily load session id into session_options

Methods
Public Class methods
new(by, env, default_options)
    # File actionpack/lib/action_controller/session/abstract_store.rb, line 15
15:         def initialize(by, env, default_options)
16:           @by = by
17:           @env = env
18:           @session_id_loaded = false
19:           merge!(default_options)
20:         end
Public Instance methods
[](key)
    # File actionpack/lib/action_controller/session/abstract_store.rb, line 22
22:         def [](key)
23:           if key == :id
24:             load_session_id! unless super(:id) || has_session_id?
25:           end
26:           super(key)
27:         end