[gn] Enable stricter build flags

src/profiler/heap-snapshot-generator.cc

 // Copyright 2013 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/profiler/heap-snapshot-generator.h"
 
 #include <utility>
 
 #include "src/api.h"
 #include "src/code-stubs.h"
@@ skipping 1697 matching lines @@
     } else {
       for (Object** p = start; p < end; p++) strong_references_.Add(*p);
     }
   }
 
   void SetCollectingAllReferences() { collecting_all_references_ = true; }
 
   void FillReferences(V8HeapExplorer* explorer) {
     DCHECK(strong_references_.length() <= all_references_.length());
     Builtins* builtins = heap_->isolate()->builtins();
+    USE(builtins);
     int strong_index = 0, all_index = 0, tags_index = 0, builtin_index = 0;
     while (all_index < all_references_.length()) {
       bool is_strong = strong_index < strong_references_.length()
           && strong_references_[strong_index] == all_references_[all_index];
       explorer->SetGcSubrootReference(reference_tags_[tags_index].tag,
                                       !is_strong,
                                       all_references_[all_index]);
       if (reference_tags_[tags_index].tag ==
           VisitorSynchronization::kBuiltins) {
         DCHECK(all_references_[all_index]->IsCode());
@@ skipping 1406 matching lines @@
   for (int i = 1; i < sorted_strings.length(); ++i) {
     writer_->AddCharacter(',');
     SerializeString(sorted_strings[i]);
     if (writer_->aborted()) return;
   }
 }
 
 
 }  // namespace internal
 }  // namespace v8