Provide private symbols through internal APIs

src/objects.h

Index: src/objects.h
diff --git a/src/objects.h b/src/objects.h
index c0835e21eb9cb5d3df0d1f5ad1e464b6d4022323..bd9689122095d6c5dfd2e49c10c8172f81ffa90c 100644
--- a/src/objects.h
+++ b/src/objects.h
@@ -359,6 +359,7 @@ const int kStubMinorKeyBits = kBitsPerInt - kSmiTagSize - kStubMajorKeyBits;
   V(SHORT_EXTERNAL_INTERNALIZED_STRING_WITH_ONE_BYTE_DATA_TYPE)                \
                                                                                \
   V(SYMBOL_TYPE)                                                               \
+                                                                               \
   V(MAP_TYPE)                                                                  \
   V(CODE_TYPE)                                                                 \
   V(ODDBALL_TYPE)                                                              \
@@ -691,7 +692,7 @@ enum InstanceType {
       | kNotInternalizedTag,
 
   // Non-string names
-  SYMBOL_TYPE = kNotStringTag,  // LAST_NAME_TYPE, FIRST_NONSTRING_TYPE
+  SYMBOL_TYPE = kNotStringTag,  // FIRST_NONSTRING_TYPE, LAST_NAME_TYPE
 
   // Objects allocated in their own spaces (never in new space).
   MAP_TYPE,
@@ -8336,6 +8337,11 @@ class Symbol: public Name {
   // [name]: the print name of a symbol, or undefined if none.
   DECL_ACCESSORS(name, Object)
 
+  DECL_ACCESSORS(flags, Smi)
+
+  // [is_private]: whether this is a private symbol.
+  DECL_BOOLEAN_ACCESSORS(is_private)
+
   // Casting.
   static inline Symbol* cast(Object* obj);
 
@@ -8345,12 +8351,14 @@ class Symbol: public Name {
 
   // Layout description.
   static const int kNameOffset = Name::kSize;
-  static const int kSize = kNameOffset + kPointerSize;
+  static const int kFlagsOffset = kNameOffset + kPointerSize;
+  static const int kSize = kFlagsOffset + kPointerSize;
 
-  typedef FixedBodyDescriptor<kNameOffset, kNameOffset + kPointerSize, kSize>
-          BodyDescriptor;
+  typedef FixedBodyDescriptor<kNameOffset, kFlagsOffset, kSize> BodyDescriptor;
 
  private:
+  static const int kPrivateBit = 0;
+
   DISALLOW_IMPLICIT_CONSTRUCTORS(Symbol);
 };