Don't lookup the cache for the result of Function::New

Since isFunctionCached condition is wrong, we lookup the cache even if
doNotCache is true. As a result, Function::New always returns null
except for the first time.

BUG=272579
R=dcarney@chromium.org, mstarzinger@chromium.org, yhirano@chromium.org

Review URL: https://codereview.chromium.org/23513048

Patch from Yusuke Suzuki <yusukesuzuki@chromium.org>.

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@16737 ce2b1a6d-e550-0410-aec6-3dcde31c8c00