parse doesn't initialize the 16-bit version of the JSC parser with defaultConstructorKind

parse doesn't initialize the 16-bit version of the JSC parser with defaultConstructorKind
https://bugs.webkit.org/show_bug.cgi?id=143170

Reviewed by Benjamin Poulain.

Assert that we never use 16-bit version of the parser to parse a default constructor
since both base and derived default constructors should be using a 8-bit string.

* parser/Parser.h:
(JSC::parse):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@182102 268f45cc-cd09-0410-ab3c-d52691b4dbfc