Make a stub constructor for parsed mappings, so that the JIT can easily infer shape / hidden class.
Make a stub constructor for parsed mappings, so that the JIT can easily infer shape / hidden class.

garysye/source-map,modulexcite/source-map,garysye/source-map,webcoding/source-map,azakhary/source-map,webcoding/source-map,modulexcite/source-map,azakhary/source-map