[regexp] simplify unanchored advance for unicode regexps.

test/mjsunit/harmony/unicode-regexp-unanchored-advance.js

Index: test/mjsunit/harmony/unicode-regexp-unanchored-advance.js
diff --git a/test/mjsunit/regress/regress-crbug-570241.js b/test/mjsunit/harmony/unicode-regexp-unanchored-advance.js
similarity index 56%
copy from test/mjsunit/regress/regress-crbug-570241.js
copy to test/mjsunit/harmony/unicode-regexp-unanchored-advance.js
index 4fecba57b5a96c77852e9b0b97ff8d2228957e01..97960e1cd30c4d7cd5b7141640b9defa06c40170 100644
--- a/test/mjsunit/regress/regress-crbug-570241.js
+++ b/test/mjsunit/harmony/unicode-regexp-unanchored-advance.js
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// Flags: --harmony-regexp-lookbehind
+// Flags: --harmony-unicode-regexps
 
-assertTrue(/(?<=12345123451234512345)/.test("12345123451234512345"));
+var s = "a".repeat(1E7) + "\u1234";
+assertEquals(["\u1234", "\u1234"], /(\u1234)/u.exec(s));