Allow objects with "" properties to stay fast.

src/heap.cc

Index: src/heap.cc
diff --git a/src/heap.cc b/src/heap.cc
index 42e56ca1eb9e2bb40498d9ea2d341c71a67f6b4e..8b94dbe0000893d49a8c0776fe05138a97ee4f0d 100644
--- a/src/heap.cc
+++ b/src/heap.cc
@@ -3307,6 +3307,12 @@ bool Heap::CreateInitialObjects() {
     if (!maybe_obj->ToObject(&obj)) return false;
   }
   Symbol::cast(obj)->set_is_private(true);
+  set_nonexistent_symbol(Symbol::cast(obj));
+
+  { MaybeObject* maybe_obj = AllocateSymbol();
+    if (!maybe_obj->ToObject(&obj)) return false;
+  }
+  Symbol::cast(obj)->set_is_private(true);
   set_elements_transition_symbol(Symbol::cast(obj));
 
   { MaybeObject* maybe_obj = SeededNumberDictionary::Allocate(this, 0, TENURED);