[regexp] break recursion in mutually recursive capture/back references.

test/mjsunit/harmony/regexp-lookbehind.js

 // 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-regexp-lookbehind
 
 // Simple fixed-length matches.
 assertEquals(["a"], "a".match(/^.(?<=a)/));
 assertNull("b".match(/^.(?<=a)/));
 assertEquals(["foo"], "foo1".match(/^f..(?<=.oo)/));
@@ skipping 139 matching lines @@
 assertEquals(["fno"], "fno".match(/^f.o(?<!foo)$/));
 assertEquals(["foooo"], "foooo".match(/^foooo(?<=fo+)$/));
 assertEquals(["foooo"], "foooo".match(/^foooo(?<=fo*)$/));
 assertEquals(["abc", "abc"], /(abc\1)/.exec("abc"));
 assertEquals(["abc", "abc"], /(abc\1)/.exec("abc\u1234"));
 assertEquals(["abc", "abc"], /(abc\1)/i.exec("abc"));
 assertEquals(["abc", "abc"], /(abc\1)/i.exec("abc\u1234"));
 var oob_subject = "abcdefghijklmnabcdefghijklmn".substr(14);
 assertNull(oob_subject.match(/(?=(abcdefghijklmn))(?<=\1)a/i));
 assertNull(oob_subject.match(/(?=(abcdefghijklmn))(?<=\1)a/));
+
+// Mutual recursive capture/back references
+assertEquals(["cacb", "a", ""], /(?<=a(.\2)b(\1)).{4}/.exec("aabcacbc"));
+assertEquals(["b", "ac", "ac"], /(?<=a(\2)b(..\1))b/.exec("aacbacb"));
+assertEquals(["x", "aa"], /(?<=(?:\1b)(aa))./.exec("aabaax"));
+assertEquals(["x", "aa"], /(?<=(?:\1|b)(aa))./.exec("aaaax"));