[runtime] Let native setters have a return value.

test/mjsunit/modules-namespace1.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.
 //
 // MODULE
 
 let ja = 42;
 export {ja as yo};
 export const bla = "blaa";
 export {foo as foo_again};
@@ skipping 14 matching lines @@
 assertEquals(
     ["bla", "foo_again", "yo", Symbol.toStringTag, Symbol.iterator],
     Reflect.ownKeys(foo));
 
 // Its "yo" property.
 assertEquals(
     {value: 42, enumerable: true, configurable: false, writable: true},
     Reflect.getOwnPropertyDescriptor(foo, "yo"));
 assertFalse(Reflect.deleteProperty(foo, "yo"));
 assertTrue(Reflect.has(foo, "yo"));
-// TODO(neis): The next three should be False.
-assertTrue(Reflect.set(foo, "yo", true));
+assertFalse(Reflect.set(foo, "yo", true));
+// TODO(neis): The next two should be False.
 assertTrue(Reflect.defineProperty(foo, "yo",
     Reflect.getOwnPropertyDescriptor(foo, "yo")));
 assertTrue(Reflect.defineProperty(foo, "yo", {}));
 assertFalse(Reflect.defineProperty(foo, "yo", {get() {return 1}}));
 assertEquals(42, Reflect.get(foo, "yo"));
 assertEquals(43, (ja++, foo.yo));
 
 // Its "foo_again" property.
 assertSame(foo, foo.foo_again);
 
@@ skipping 51 matching lines @@
   assertFalse(Reflect.has(foo, key));
 }
 
 // The actual star import that we are testing. Namespace imports are
 // initialized before evaluation.
 import * as foo from "modules-namespace1.js";
 
 // There can be only one namespace object.
 import * as bar from "modules-namespace1.js";
 assertSame(foo, bar);