Don't flush code for generator functions.

R=mstarzinger@chromium.org
BUG=v8:2681
TEST=mjsunit/regress/regress-2681

Review URL: https://codereview.chromium.org/14731023

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@14649 ce2b1a6d-e550-0410-aec6-3dcde31c8c00