[es6] Correct length for functions with default parameters

test/mjsunit/harmony/destructuring.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-destructuring --harmony-arrow-functions
 // Flags: --harmony-default-parameters --harmony-rest-parameters
 
 (function TestObjectLiteralPattern() {
   var { x : x, y : y } = { x : 1, y : 2 };
   assertEquals(1, x);
@@ skipping 935 matching lines @@
   assertEquals(6, f8(5, 6));
 }());
 
 
 (function TestForInOfTDZ() {
   assertThrows("'use strict'; let x = {}; for (let [x, y] of {x});", ReferenceError);
   assertThrows("'use strict'; let x = {}; for (let [y, x] of {x});", ReferenceError);
   assertThrows("'use strict'; let x = {}; for (let [x, y] in {x});", ReferenceError);
   assertThrows("'use strict'; let x = {}; for (let [y, x] in {x});", ReferenceError);
 }());
+
+
+(function TestFunctionLength() {
+   assertEquals(1, (function({}) {}).length);
+   assertEquals(1, (function([]) {}).length);
+   assertEquals(1, (function({x}) {}).length);
+   assertEquals(1, (function({}, ...a) {}).length);
+   assertEquals(1, (function({x}, {y} = {}) {}).length);
+   assertEquals(1, (function({x}, {y} = {}, ...a) {}).length);
+   assertEquals(2, (function(x, {y}, {z} = {}) {}).length);
+   assertEquals(2, (function({x}, {}, {z} = {}, ...a) {}).length);
+   assertEquals(1, (function(x, {y} = {}, {z}) {}).length);
+   assertEquals(1, (function({x}, {y} = {}, {z}, ...a) {}).length);
+   assertEquals(1, (function(x, {y} = {}, {z}, {v} = {}) {}).length);
+   assertEquals(1, (function({x}, {y} = {}, {z}, {v} = {}, ...a) {}).length);
+})();