[es6] Correct length for functions with default parameters

test/mjsunit/harmony/default-parameters.js

Index: test/mjsunit/harmony/default-parameters.js
diff --git a/test/mjsunit/harmony/default-parameters.js b/test/mjsunit/harmony/default-parameters.js
index 3be5916d9bf5553265889489f2b143b51cdc2928..0d87b0371217876779656f6a32568c065cecd365 100644
--- a/test/mjsunit/harmony/default-parameters.js
+++ b/test/mjsunit/harmony/default-parameters.js
@@ -418,15 +418,14 @@
 
 
 (function TestFunctionLength() {
-  // TODO(rossberg): Fix arity.
-  // assertEquals(0, (function(x = 1) {}).length);
-  // assertEquals(0, (function(x = 1, ...a) {}).length);
-  // assertEquals(1, (function(x, y = 1) {}).length);
-  // assertEquals(1, (function(x, y = 1, ...a) {}).length);
-  // assertEquals(2, (function(x, y, z = 1) {}).length);
-  // assertEquals(2, (function(x, y, z = 1, ...a) {}).length);
-  // assertEquals(1, (function(x, y = 1, z) {}).length);
-  // assertEquals(1, (function(x, y = 1, z, ...a) {}).length);
-  // assertEquals(1, (function(x, y = 1, z, v = 2) {}).length);
-  // assertEquals(1, (function(x, y = 1, z, v = 2, ...a) {}).length);
+   assertEquals(0, (function(x = 1) {}).length);
+   assertEquals(0, (function(x = 1, ...a) {}).length);
+   assertEquals(1, (function(x, y = 1) {}).length);
+   assertEquals(1, (function(x, y = 1, ...a) {}).length);
+   assertEquals(2, (function(x, y, z = 1) {}).length);
+   assertEquals(2, (function(x, y, z = 1, ...a) {}).length);
+   assertEquals(1, (function(x, y = 1, z) {}).length);
+   assertEquals(1, (function(x, y = 1, z, ...a) {}).length);
+   assertEquals(1, (function(x, y = 1, z, v = 2) {}).length);
+   assertEquals(1, (function(x, y = 1, z, v = 2, ...a) {}).length);
 })();