[regexp] Don't cache exec method in Regexp.proto[@@split]

test/mjsunit/regress/regress-5351.js

Index: test/mjsunit/regress/regress-5351.js
diff --git a/test/mjsunit/regress/regress-5351.js b/test/mjsunit/regress/regress-5351.js
new file mode 100644
index 0000000000000000000000000000000000000000..c9e6d3153a6e8f1c8fd9c096d32759b172f37c27
--- /dev/null
+++ b/test/mjsunit/regress/regress-5351.js
@@ -0,0 +1,12 @@
+// Copyright 2016 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.
+
+var re = /[bc]/;
+var str = "baba";
+
+assertEquals(["", "a", "a"], str.split(re));
+
+// Force slow path.
+re.exec = (string) => RegExp.prototype.exec.call(re, string);
+assertEquals(["", "a", "a"], str.split(re));