[runtime] Let native setters have a return value.

test/mjsunit/modules-namespace1.js

Index: test/mjsunit/modules-namespace1.js
diff --git a/test/mjsunit/modules-namespace1.js b/test/mjsunit/modules-namespace1.js
index beb469efa4e1651a257c1ccf6ca7130d5df5b201..227b9c8a4c822f43e8ed1a4a5f51a5db62c986cf 100644
--- a/test/mjsunit/modules-namespace1.js
+++ b/test/mjsunit/modules-namespace1.js
@@ -32,8 +32,8 @@ assertEquals(
     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", {}));