deps: port d9e9d9f to deps/v8z

Original commit message:

deps: backport e7cc609 from upstream V8

This is part 1/2 of the fixes from v8:4871. This fixes a segfault in
verify-heap.

Original commit message:
  [crankshaft] Write fillers for folded old space allocations during verify-heap

  If we don't write fillers, we crash during PagedSpace verification when we try
  to iterate over dead memory (unused folded allocation slots).

  BUG=v8:4871,chromium:580959
  LOG=N

  Review URL: https://codereview.chromium.org/1837163002

  Cr-Commit-Position: refs/heads/master@{#35097}

Fixes: nodejs/node#5900
V8-Bug: https://bugs.chromium.org/p/v8/issues/detail?id=4871

PR-URL: nodejs/node#7303
Reviewed-By: Michaël Zasso <[email protected]>
Reviewed-By: Ben Noordhuis <[email protected]>
Reviewed-By: Fedor Indutny <[email protected]>
Reviewed-By: Myles Borins <[email protected]>

deps/v8z/src/hydrogen-instructions.cc

@@ -3827,12 +3827,12 @@ bool HAllocate::HandleSideEffectDominator(GVNFlag side_effect,
     }
   }
 
-  bool keep_new_space_iterable = FLAG_log_gc || FLAG_heap_stats;
+  bool keep_heap_iterable = FLAG_log_gc || FLAG_heap_stats;
 #ifdef VERIFY_HEAP
-  keep_new_space_iterable = keep_new_space_iterable || FLAG_verify_heap;
+  keep_heap_iterable = keep_heap_iterable || FLAG_verify_heap;
 #endif
 
-  if (keep_new_space_iterable && dominator_allocate->IsNewSpaceAllocation()) {
+  if (keep_heap_iterable) {
     dominator_allocate->MakePrefillWithFiller();
   } else {
     // TODO(hpayer): This is a short-term hack to make allocation mementos