Harvesting maps from the stub cache for megamorphic ICs is both slow
(linear in the size of the stub cache) and imprecise (as it finds all
maps that have a cached handler for the given property name).
In the canonical megamorphic situation, this type feedback is useless
anyway. The interesting case is when we can filter it down to a single
map; however in these cases it is often possible to derive this map
just by looking at the HGraph, which is both faster and more reliable.

Review URL: https://codereview.chromium.org/1669213003

Cr-Commit-Position: refs/heads/master@{#33998}