Additionally, this enables the use of a CHECK_ALIVE macro instead of
copy-n-paste code at one place.

This CL is part of a series of several yak-shaving CLs to prepare the inlining
of JavaScript accessors.

Review URL: https://chromiumcodereview.appspot.com/10783017

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@12093 ce2b1a6d-e550-0410-aec6-3dcde31c8c00