Provide private symbols through internal APIs

include/v8.h

Index: include/v8.h
diff --git a/include/v8.h b/include/v8.h
index 44a74ed5fea97282ce307cafd3d88df161da1adc..299472a04fc1c48390ff4d88f60b3cf31ea84dc2 100644
--- a/include/v8.h
+++ b/include/v8.h
@@ -114,6 +114,7 @@ class String;
 class StringObject;
 class Symbol;
 class SymbolObject;
+class Private;
 class Uint32;
 class Utils;
 class Value;
@@ -1926,11 +1927,9 @@ class V8_EXPORT Symbol : public Primitive {
   // Returns the print name string of the symbol, or undefined if none.
   Local<Value> Name() const;
 
-  // Create a symbol without a print name.
-  static Local<Symbol> New(Isolate* isolate);
-
-  // Create a symbol with a print name.
-  static Local<Symbol> New(Isolate *isolate, const char* data, int length = -1);
+  // Create a symbol. If data is not NULL, it will be used as a print name.
+  static Local<Symbol> New(
+      Isolate *isolate, const char* data = NULL, int length = -1);
 
   V8_INLINE static Symbol* Cast(v8::Value* obj);
  private:
@@ -1940,6 +1939,25 @@ class V8_EXPORT Symbol : public Primitive {
 
 
 /**
+ * A private symbol
+ *
+ * This is an experimental feature. Use at your own risk.
+ */
+class V8_EXPORT Private : public Data {
+ public:
+  // Returns the print name string of the private symbol, or undefined if none.
+  Local<Value> Name() const;
+
+  // Create a private symbol. If data is not NULL, it will be the print name.
+  static Local<Private> New(
+      Isolate *isolate, const char* data = NULL, int length = -1);
+
+ private:
+  Private();
+};
+
+
+/**
  * A JavaScript number value (ECMA-262, 4.3.20)
  */
 class V8_EXPORT Number : public Primitive {
@@ -2109,6 +2127,17 @@ class V8_EXPORT Object : public Value {
                            AccessControl settings = DEFAULT);
 
   /**
+   * Functionality for private properties.
+   * This is an experimental feature, use at your own risk.
+   * Note: Private properties are inherited. Do not rely on this, since it may
+   * change.
+   */
+  bool HasPrivate(Handle<Private> key);
+  bool SetPrivate(Handle<Private> key, Handle<Value> value);
+  bool DeletePrivate(Handle<Private> key);
+  Local<Value> GetPrivate(Handle<Private> key);
+
+  /**
    * Returns an array containing the names of the enumerable properties
    * of this object, including properties from prototype objects.  The
    * array returned by this method contains the same values as would