This moves the clearing of all optimized code maps out of the GC and
into the debugger to where it is actually required. The main goal here
is to simplify the logic in the already complex visitor for our shared
function info objects.

R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/1423713018

Cr-Commit-Position: refs/heads/master@{#31888}