[api] Default native data property setter to replace the setter if the property is writable.

test/mjsunit/regress/regress-crbug-580584.js

+// 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.
+
+function f() { return arguments }
+
+// Reconfiguring function.name should update both the attributes and the value.
+Object.defineProperty(f, "name", {
+  writable: true, configurable: true, value: 10});
+assertEquals({value: 10, writable: true, enumerable: false, configurable: true},
+             Object.getOwnPropertyDescriptor(f, "name"));
+
+var args = f();
+
+// Setting a value for arguments[Symbol.iterator] should not affect the
+// attributes.
+args[Symbol.iterator] = 10;
+assertEquals({value: 10, writable: true, configurable: true, enumerable: false},
+             Object.getOwnPropertyDescriptor(args, Symbol.iterator));