Make sure that NormalizeElements and ShouldConvertToFastElements are based on the same values

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 42a1c7e317863d57cf3f406e3ad099ec44793053..7905f39c17c2d52a049231d4b3b87417c276d5a0 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -14646,6 +14646,8 @@ static bool ShouldConvertToFastElements(JSObject* object,
 
   uint32_t dictionary_size = static_cast<uint32_t>(dictionary->Capacity()) *
                              SeededNumberDictionary::kEntrySize;
+
+  // Turn fast if the dictionary only saves 50% space.
   return 2 * dictionary_size >= *new_capacity;
 }