MIPS: Turn RegExpConstructResultStub into a HydrogenCodeStub.

Port r18902 (ba394fbc)

Original commit message:
This has the additional benefit that it is now possible to
inline the RegExpResult construction code into Hydrogen
builtins.

BUG=
R=plind44@gmail.com

Review URL: https://codereview.chromium.org/149863003

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@18934 ce2b1a6d-e550-0410-aec6-3dcde31c8c00