[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}

src/crankshaft/hydrogen-instructions.cc

@@ -3254,12 +3254,12 @@ 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