This adds explicit setters for the SharedFunctionInfo::function_data
field. Such setters are safer because they allow for explicit checking
of which values are allowed, and they improve readability because the
intended semantics become clear for each call-site. Also fix a cctest
case along the way.

R=rmcilroy@chromium.org

Review URL: https://codereview.chromium.org/1730853005

Cr-Commit-Position: refs/heads/master@{#34297}