[runtime] Let native setters have a return value.

test/mjsunit/es6/reflect.js

Index: test/mjsunit/es6/reflect.js
diff --git a/test/mjsunit/es6/reflect.js b/test/mjsunit/es6/reflect.js
index d597a78901ad35a081d167a87c651cad01f86c0c..9e21717a994a0a38f65ded7d85a750e64473fc78 100644
--- a/test/mjsunit/es6/reflect.js
+++ b/test/mjsunit/es6/reflect.js
@@ -273,6 +273,14 @@ function prepare(target) {
 })();
 
 
+(function testReflectSetArrayLength() {
+  var y = [];
+  Object.defineProperty(y, 0, {value: 42, configurable: false});
+  assertFalse(Reflect.set(y, 'length', 0));
+  assertTrue(Reflect.set(y, 'length', 2));
+})();
+
+
 
 ////////////////////////////////////////////////////////////////////////////////
 // Reflect.has
@@ -352,6 +360,14 @@ function prepare(target) {
 })();
 
 
+(function testReflectDefinePropertyArrayLength() {
+  var y = [];
+  Object.defineProperty(y, 0, {value: 42, configurable: false});
+  assertFalse(Reflect.defineProperty(y, 'length', {value: 0}));
+  assertTrue(Reflect.defineProperty(y, 'length', {value: 2}));
+})();
+
+
 // See reflect-define-property.js for further tests.