This separates the post-processing step for optimized code maps out of
the CodeFlusher. It uses the complete SharedFunctionInfo::Iterator to
visit all candidates instead of gathering candidates during marking.

Gathering candidates during marking no longer makes sense, now that the
majority of SharedFunctionInfo objects will hold such an optimized code
map. Also it reduces complexity of the implementation. Also conflating
this mechanism with "code flushing" was confusing.

R=ulan@chromium.org

Review URL: https://codereview.chromium.org/1426953006

Cr-Commit-Position: refs/heads/master@{#31830}