The 'selected' option is not doing what it should do.
The expected behavior is to pass the value selected by default for the options_from_collection_for_select method
This has 2 effects:
1. RoutesProxy is CRAZY faster because it's no longer creating a new
Module each time method_missing is hit.
2. It bypasses an existing bug in ruby that makes `class << obj` unsafe
to be used in threading contexts.
The cause by which the test suite for the mysql adapter broke in 1502cae
(reverted 89ba5bb) is because the precision was not extracted.
The rounding problem in mysql adapter has not been fixed, but `mysql_56`
helper tested only mysql2 adapter, its behavior was not apparent.
Moves `X-Request-ID`, `action_dispatch.request_id` and
`HTTP_X_REQUEST_ID` strings to constants and freezes them.
We are freezing these strings to reduce the number of allocations in
Rails integration tests. The tests are spending a lot of time in GC and
this reduces the amount of time spent from 12% to 9% (in combination
with Rack PR that also freezes some strings).
Number of allocations before this change: 1030722
Number of allocations after this change: 967722
