Use StringJoiner to create the JSString of arrayProtoFuncToString
https://bugs.webkit.org/show_bug.cgi?id=114779

Patch by Benjamin Poulain <bpoulain@apple.com> on 2013-04-18
Reviewed by Geoffrey Garen.

The function arrayProtoFuncToString was just a glorified JSStringJoiner.
This patch replaces it by JSStringJoiner to simplify the code and enjoy any optimization
made on JSStringJoiner.

For some reason, this makes the execution 3.4% faster, despite having almost identical code.

* runtime/ArrayPrototype.cpp:
(JSC::arrayProtoFuncToString):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@148721 268f45cc-cd09-0410-ab3c-d52691b4dbfc