Force SharedFunctionInfo::name() to be a flat string

test/mjsunit/regress/regress-4659.js

Index: test/mjsunit/regress/regress-4659.js
diff --git a/test/message/arrow-invalid-rest-2.js b/test/mjsunit/regress/regress-4659.js
similarity index 58%
copy from test/message/arrow-invalid-rest-2.js
copy to test/mjsunit/regress/regress-4659.js
index 3517803d30256b09e78a1aa1f43817e733dc060e..ff436bec1b07d6a708ddd0a0c454ada3c353985c 100644
--- a/test/message/arrow-invalid-rest-2.js
+++ b/test/mjsunit/regress/regress-4659.js
@@ -2,7 +2,11 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 //
-//
+// Flags: --harmony-function-name
 
-var f = (a, ...x = 10) => x;
-f(1, 2, 3, 4, 5);
+var obj = {
+  get longerName(){
+    return 42;
+  }
+};
+assertEquals(42, obj.longerName);