This avoids regenerating baseline code for a closure when such code
already exists for the shared function info. This is also important
because the baseline code might contain deoptimization support.

R=rmcilroy@chromium.org
BUG=chromium:606376
LOG=n

Review URL: https://codereview.chromium.org/1916833002

Cr-Commit-Position: refs/heads/master@{#35785}