Provide private symbols through internal APIs

src/heap.cc

Index: src/heap.cc
diff --git a/src/heap.cc b/src/heap.cc
index fa358c53929127218fbd4fd719d5bec8d3bab3b0..9c7c8483f7b7527496de6810f08b3164aff4a9d8 100644
--- a/src/heap.cc
+++ b/src/heap.cc
@@ -3282,11 +3282,13 @@ bool Heap::CreateInitialObjects() {
   { MaybeObject* maybe_obj = AllocateSymbol();
     if (!maybe_obj->ToObject(&obj)) return false;
   }
+  Symbol::cast(obj)->set_is_private(true);
   set_frozen_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);
@@ -3298,6 +3300,7 @@ bool Heap::CreateInitialObjects() {
   { MaybeObject* maybe_obj = AllocateSymbol();
     if (!maybe_obj->ToObject(&obj)) return false;
   }
+  Symbol::cast(obj)->set_is_private(true);
   set_observed_symbol(Symbol::cast(obj));
 
   // Handling of script id generation is in Factory::NewScript.
@@ -5595,12 +5598,22 @@ MaybeObject* Heap::AllocateSymbol() {
   Symbol::cast(result)->set_hash_field(
       Name::kIsNotArrayIndexMask | (hash << Name::kHashShift));
   Symbol::cast(result)->set_name(undefined_value());
+  Symbol::cast(result)->set_flags(Smi::FromInt(0));
 
-  ASSERT(result->IsSymbol());
+  ASSERT(!Symbol::cast(result)->is_private());
   return result;
 }
 
 
+MaybeObject* Heap::AllocatePrivateSymbol() {
+  MaybeObject* maybe = AllocateSymbol();
+  Symbol* symbol;
+  if (!maybe->To(&symbol)) return maybe;
+  symbol->set_is_private(true);
+  return symbol;
+}
+
+
 MaybeObject* Heap::AllocateNativeContext() {
   Object* result;
   { MaybeObject* maybe_result =