Implement sealing, freezing, and related functions for proxies.

src/objects.cc

Index: src/objects.cc
diff --git a/src/objects.cc b/src/objects.cc
index 26ab64552fc344fff7be569d3f43b365650c4d6f..2f62b9021421bf50ddb1db7100033091c60b108c 100644
--- a/src/objects.cc
+++ b/src/objects.cc
@@ -2301,6 +2301,18 @@ MUST_USE_RESULT PropertyAttributes JSProxy::GetPropertyAttributeWithHandler(
 }
 
 
+void JSProxy::Fix() {
+  Isolate* isolate = GetIsolate();
+  HandleScope scope(isolate);
+  Handle<JSReceiver> self(this);
+
+  isolate->factory()->BecomeJSObject(self);
+  ASSERT(IsJSObject());
+  // TODO(rossberg): recognize function proxies.
+}
+
+
+
 MaybeObject* JSObject::SetPropertyForResult(LookupResult* result,
                                             String* name,
                                             Object* value,