Implement sealing, freezing, and related functions for proxies.

src/factory.cc

Index: src/factory.cc
diff --git a/src/factory.cc b/src/factory.cc
index 9ba48ee5024fa1cb3a59c85864ff88604e8339b0..ecf9432952e14926446acd4b0bbc9b9b91be9436 100644
--- a/src/factory.cc
+++ b/src/factory.cc
@@ -892,6 +892,13 @@ Handle<JSProxy> Factory::NewJSProxy(Handle<Object> handler,
 }
 
 
+void Factory::BecomeJSObject(Handle<JSReceiver> object) {
+  CALL_HEAP_FUNCTION_VOID(
+      isolate(),
+      isolate()->heap()->ReinitializeJSReceiverAsJSObject(*object));
+}
+
+
 Handle<SharedFunctionInfo> Factory::NewSharedFunctionInfo(
     Handle<String> name,
     int number_of_literals,