Add "own" symbols support.

src/factory.h

 // Copyright 2014 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_FACTORY_H_
 #define V8_FACTORY_H_
 
 #include "src/isolate.h"
 
 namespace v8 {
@@ skipping 203 matching lines @@
   // because we cannot change the underlying buffer.  Note that these strings
   // are backed by a string resource that resides outside the V8 heap.
   MUST_USE_RESULT MaybeHandle<String> NewExternalStringFromAscii(
       const ExternalAsciiString::Resource* resource);
   MUST_USE_RESULT MaybeHandle<String> NewExternalStringFromTwoByte(
       const ExternalTwoByteString::Resource* resource);
 
   // Create a symbol.
   Handle<Symbol> NewSymbol();
   Handle<Symbol> NewPrivateSymbol();
+  Handle<Symbol> NewPrivateOwnSymbol();
 
   // Create a global (but otherwise uninitialized) context.
   Handle<Context> NewNativeContext();
 
   // Create a global context.
   Handle<Context> NewGlobalContext(Handle<JSFunction> function,
                                    Handle<ScopeInfo> scope_info);
 
   // Create a module context.
   Handle<Context> NewModuleContext(Handle<ScopeInfo> scope_info);
@@ skipping 467 matching lines @@
                                  PretenureFlag pretenure = TENURED);
 
   Handle<JSFunction> NewFunction(Handle<Map> map,
                                  Handle<String> name,
                                  MaybeHandle<Code> maybe_code);
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_FACTORY_H_