Separate String.prototype.replace into RegExp.prototype[Symbol.replace]

test/mjsunit/harmony/string-replace.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-subclass
+
+var pattern = {
+  [Symbol.replace]: (string, newValue) => string + newValue
+};
+// Check object coercible fails.
+assertThrows(() => String.prototype.replace.call(null, pattern, "x"),
+             TypeError);
+// Override is called.
+assertEquals("abcdex", "abcde".replace(pattern, "x"));
+// Non-callable override.
+pattern[Symbol.replace] = "dumdidum";
+assertThrows(() => "abcde".replace(pattern, "x"), TypeError);
+
+assertEquals("[Symbol.replace]", RegExp.prototype[Symbol.replace].name);