Ensure that JSProxy::Fix gives the generated JSObject map a constructor

test/mjsunit/harmony/regress/regress-405844.js

Index: test/mjsunit/harmony/regress/regress-405844.js
diff --git a/test/mjsunit/harmony/regress/regress-405844.js b/test/mjsunit/harmony/regress/regress-405844.js
new file mode 100644
index 0000000000000000000000000000000000000000..fbe7310d7966385cd22d9e975c0b5cbedb05e22d
--- /dev/null
+++ b/test/mjsunit/harmony/regress/regress-405844.js
@@ -0,0 +1,13 @@
+// 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.
+//
+// Flags: --harmony-proxies
+
+var proxy = Proxy.create({ fix: function() { return {}; } });
+Object.preventExtensions(proxy);
+Object.observe(proxy, function(){});
+
+var functionProxy = Proxy.createFunction({ fix: function() { return {}; } }, function(){});
+Object.preventExtensions(functionProxy);
+Object.observe(functionProxy, function(){});