[gn] Enable stricter build flags

src/objects.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/objects.h"
 
 #include <cmath>
 #include <iomanip>
 #include <memory>
 #include <sstream>
@@ skipping 12333 matching lines @@
   Object* maybe_cell = proto_info->validity_cell();
   if (maybe_cell->IsCell()) {
     // Just set the value; the cell will be replaced lazily.
     Cell* cell = Cell::cast(maybe_cell);
     cell->set_value(Smi::FromInt(Map::kPrototypeChainInvalid));
   }
 
   WeakFixedArray::Iterator iterator(proto_info->prototype_users());
   // For now, only maps register themselves as users.
   Map* user;
-  while ((user = iterator.Next<Map>())) {
+  while ((user = iterator.Next<Map>()) != nullptr) {
     // Walk the prototype chain (backwards, towards leaf objects) if necessary.
     InvalidatePrototypeChainsInternal(user);
   }
 }
 
 
 // static
 void JSObject::InvalidatePrototypeChains(Map* map) {
   DisallowHeapAllocation no_gc;
   InvalidatePrototypeChainsInternal(map);
@@ skipping 961 matching lines @@
 #endif
     Handle<WeakCell> cell = isolate->factory()->NewWeakCell(shared);
     list->set(shared->function_literal_id(), *cell);
   } else {
     Handle<Object> list = isolate->factory()->noscript_shared_function_infos();
 
 #ifdef DEBUG
     if (FLAG_enable_slow_asserts) {
       WeakFixedArray::Iterator iterator(*list);
       SharedFunctionInfo* next;
-      while ((next = iterator.Next<SharedFunctionInfo>())) {
+      while ((next = iterator.Next<SharedFunctionInfo>()) != nullptr) {
         DCHECK_NE(next, *shared);
       }
     }
 #endif  // DEBUG
 
     list = WeakFixedArray::Add(list, shared);
 
     isolate->heap()->SetRootNoScriptSharedFunctionInfos(*list);
   }
 
@@ skipping 6940 matching lines @@
       // depend on this.
       return DICTIONARY_ELEMENTS;
     }
     DCHECK_LE(kind, LAST_ELEMENTS_KIND);
     return kind;
   }
 }
 
 }  // namespace internal
 }  // namespace v8