[gn] Enable stricter build flags

src/profiler/heap-snapshot-generator.cc

Index: src/profiler/heap-snapshot-generator.cc
diff --git a/src/profiler/heap-snapshot-generator.cc b/src/profiler/heap-snapshot-generator.cc
index eaa165d24b1f6aa7cfadfd98bea597a785a47ce7..4cb6d7273556ab2b57218591683fc31040caaa9d 100644
--- a/src/profiler/heap-snapshot-generator.cc
+++ b/src/profiler/heap-snapshot-generator.cc
@@ -1715,6 +1715,7 @@ class RootsReferencesExtractor : public ObjectVisitor {
   void FillReferences(V8HeapExplorer* explorer) {
     DCHECK(strong_references_.length() <= all_references_.length());
     Builtins* builtins = heap_->isolate()->builtins();
+    USE(builtins);

[jgruber, 2017/03/17 13:21:20]

Not sure what's up with this, produces an initialized but unused warning. Maybe
a compiler bug?

     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()