Make AstRawString deduplication encoding-agnostic.

test/mjsunit/regress/regress-4450.js

Index: test/mjsunit/regress/regress-4450.js
diff --git a/test/message/arrow-bare-rest-param.js b/test/mjsunit/regress/regress-4450.js
similarity index 61%
copy from test/message/arrow-bare-rest-param.js
copy to test/mjsunit/regress/regress-4450.js
index bd5761f4e8849cba109c8d111f6526f9107c736e..31ff4f19c26d7704f49eef42dc80c187bbfe55b3 100644
--- a/test/message/arrow-bare-rest-param.js
+++ b/test/mjsunit/regress/regress-4450.js
@@ -1,7 +1,8 @@
 // Copyright 2015 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-rest-parameters
 
-...x => 10
+({})['foobar\u2653'.slice(0, 6)] = null;
+var x;
+eval('x = function foobar() { return foobar };');
+x();