Port r16806 (9f102a8)

Original commit message:
This renames the method to LookupNumberStringCache() and puts it into
the MacroAssembler in preparation of the NumberToStringStub Hydrogen
conversion.

BUG=
R=plind44@gmail.com

Review URL: https://codereview.chromium.org/23526072

Patch from Balazs Kilvady <kilvadyb@homejinni.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@16839 ce2b1a6d-e550-0410-aec6-3dcde31c8c00