Port r14931 (a914442)

Original commit message:
This removes the FACTORY helper macro to avoid accidental TLS access
when using the factory. Most internal code has access to the Isolate by
now whereas tests which are not performance critical still heavily use
TLS access through explicit Isolate::Current() calls.

BUG=

Review URL: https://codereview.chromium.org/15994011
Patch from Balazs Kilvady <kilvadyb@homejinni.com>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@14942 ce2b1a6d-e550-0410-aec6-3dcde31c8c00