I noticed these files all had strings such as "", " ", "_" that were
allocated each time some common methods were called, over 1000x on a
page in my app. This comment freezes all of these strings such that
they're only allocated once, saving many KB of memory allocation.
* MockController#polymorphic_mappings
* Database-specific types (e.g., :text) moved from ActiveModel to
ActiveRecord so the type_for_attribute helper needed adjustment.
Dillon Welch