This fixes a corner case that happens when JSFunctions are enqueued as
code flushing candidates but their respective SharedFunctionInfo isn't.
If the JSFunction gets evicted due to optimization the code slot in the
SharedFunctionInfo will never be recorded in the slots buffer.

R=hpayer@chromium.org
BUG=chromium:168801
TEST=cctest/test-heap/Regress168801

Review URL: https://codereview.chromium.org/11896064

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@13481 ce2b1a6d-e550-0410-aec6-3dcde31c8c00