Rewrite decodeURL as builtin function, remove now unused runtime functions.

test/mjsunit/regress/regress-crbug-612109.js

Index: test/mjsunit/regress/regress-crbug-612109.js
diff --git a/test/mjsunit/regress/regress-crbug-612109.js b/test/mjsunit/regress/regress-crbug-612109.js
new file mode 100644
index 0000000000000000000000000000000000000000..202bd96c774e63d89810ea4545c2212d54f97a63
--- /dev/null
+++ b/test/mjsunit/regress/regress-crbug-612109.js
@@ -0,0 +1,8 @@
+// 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.
+
+
+s = "string for triggering osr in __f_0";
+for (var i = 0; i < 16; i++) s = s + s;
+decodeURI(encodeURI(s));