Ideally the JSInliner should not be concerned with JSFunction's at all,
but only look at the SharedFunctionInfo. This reduces the uses of the
concrete closure to two remaining cases, which we plan to fix soonish
too.

R=jarin@chromium.org

Review URL: https://codereview.chromium.org/1714803002

Cr-Commit-Position: refs/heads/master@{#34135}