[gn] Enable stricter build flags

src/extensions/statistics-extension.cc

 // Copyright 2012 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/extensions/statistics-extension.h"
 
 #include "src/counters.h"
 #include "src/heap/heap-inl.h"
 #include "src/isolate.h"
 
@@ skipping 126 matching lines @@
   }
 
   AddNumber64(args.GetIsolate(), result, heap->external_memory(),
               "amount_of_external_allocated_memory");
   args.GetReturnValue().Set(result);
 
   HeapIterator iterator(reinterpret_cast<Isolate*>(args.GetIsolate())->heap());
   HeapObject* obj;
   int reloc_info_total = 0;
   int source_position_table_total = 0;
-  while ((obj = iterator.next())) {
+  while ((obj = iterator.next()) != nullptr) {
     if (obj->IsCode()) {
       Code* code = Code::cast(obj);
       reloc_info_total += code->relocation_info()->Size();
       ByteArray* source_position_table = code->source_position_table();
       if (source_position_table->length() > 0) {
         source_position_table_total += code->source_position_table()->Size();
       }
     } else if (obj->IsBytecodeArray()) {
       source_position_table_total +=
           BytecodeArray::cast(obj)->source_position_table()->Size();
     }
   }
 
   AddNumber(args.GetIsolate(), result, reloc_info_total,
             "reloc_info_total_size");
   AddNumber(args.GetIsolate(), result, source_position_table_total,
             "source_position_table_total_size");
 }
 
 }  // namespace internal
 }  // namespace v8