Call constructor of ConstraintMapping.
Call constructor of ConstraintMapping.

Last refactoring removed call to constructor of ConstraintMapping, and
broke a build.

canassa/http.async.client,michaelneale/http.async.client,diamondap/http.async.client,oliyh/http.async.client,josephwilk/http.async.client,bpoweski/http.async.client