String.prototype.anchor and others should not cause side effects.

test/mjsunit/regress/regress-5836.js

Index: test/mjsunit/regress/regress-5836.js
diff --git a/test/mjsunit/regress/regress-5836.js b/test/mjsunit/regress/regress-5836.js
new file mode 100644
index 0000000000000000000000000000000000000000..0c8d1193c8b90d241f61a377cc637a75d815ea0e
--- /dev/null
+++ b/test/mjsunit/regress/regress-5836.js
@@ -0,0 +1,7 @@
+// 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 previous = RegExp.lastMatch;
+'hello world'.anchor('"hi"');
+assertEquals(previous, RegExp.lastMatch);