Implement ES6 symbol registry and predefined symbols

src/runtime.cc

Index: src/runtime.cc
diff --git a/src/runtime.cc b/src/runtime.cc
index 762b7a58b9f28fea2dd57f0d6b3f35bdfd7971cd..f3cf01bf265a711cbfb6f2d57280ae48dc6edec6 100644
--- a/src/runtime.cc
+++ b/src/runtime.cc
@@ -636,6 +636,13 @@ RUNTIME_FUNCTION(MaybeObject*, Runtime_SymbolDescription) {
 }
 
 
+RUNTIME_FUNCTION(MaybeObject*, Runtime_SymbolRegistry) {
+  SealHandleScope shs(isolate);
+  ASSERT(args.length() == 0);
+  return isolate->heap()->symbol_registry();
+}
+
+
 RUNTIME_FUNCTION(MaybeObject*, Runtime_SymbolIsPrivate) {
   SealHandleScope shs(isolate);
   ASSERT(args.length() == 1);