Revert "[heap, runtime] Fix data race in prototype map transition during"

This reverts commit d8846ffd.

Reason: the fix doesn't work, the proper fix is to not mutate the map.

BUG=chromium:694255
TBR=ishell@chromium.org

Change-Id: Iebef7cd01081145c172902727e0035a8745703b7
Reviewed-on: https://chromium-review.googlesource.com/594727Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47020}

src/objects.cc

@@ -4178,11 +4178,6 @@ void JSObject::MigrateToMap(Handle<JSObject> object, Handle<Map> new_map,
   } else if (!new_map->is_dictionary_map()) {
     MigrateFastToFast(object, new_map);
     if (old_map->is_prototype_map()) {
-      DisallowHeapAllocation no_allocation;
-      // Ensure that the object is marked because its old map is going
-      // to drop the descriptor array and the layout descriptor, which
-      // is unsafe for the concurrent marker.
-      object->GetHeap()->NotifyObjectLayoutChange(*object, no_allocation);
       DCHECK(!old_map->is_stable());
       DCHECK(new_map->is_stable());
       // Clear out the old descriptor array to avoid problems to sharing
@@ -4193,11 +4188,6 @@ void JSObject::MigrateToMap(Handle<JSObject> object, Handle<Map> new_map,
       // Ensure that no transition was inserted for prototype migrations.
       DCHECK_EQ(0, TransitionsAccessor(old_map).NumberOfTransitions());
       DCHECK(new_map->GetBackPointer()->IsUndefined(new_map->GetIsolate()));
-#ifdef VERIFY_HEAP
-      // When verify heap is on, NotifyObjectLayoutChange checks that
-      // it is followed by VerifyObjectLayoutChange after the map change.
-      object->GetHeap()->VerifyObjectLayoutChange(*object, *new_map);
-#endif
     }
   } else {
     MigrateFastToSlow(object, new_map, expected_additional_properties);