So far the for-in slow path in Crankshaft unconditionally called
%ForInFilter for every iteration of the for-in loop, without paying
attention to the possible enum cache equipped receiver map. So even
though we iterate the enum cache FixedArray associated with the map
we don't check the map, but always go to %ForInFilter. This would be
perfectly fine if the enum cache FixedArray would be immutable, but
due to some funny GC/runtime interaction kicking in, the enum cache
can be right trimmed while we are iterating it, and the only way to
detect this is to ensure that we check the map when accessing the
enum cache.
BUG=v8:3650,v8:4715
LOG=n
Review URL: https://codereview.chromium.org/1650493002
Cr-Commit-Position: refs/heads/master@{#33599}
