[es6] Fix length property of collection constructors

test/mjsunit/es6/collections.js

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 328 matching lines @@
 TestPrototype(Map);
 TestPrototype(WeakMap);
 TestPrototype(WeakSet);
 
 
 // Test constructor property of the Set, Map, WeakMap and WeakSet prototype.
 function TestConstructor(C) {
   assertFalse(C === Object.prototype.constructor);
   assertSame(C, C.prototype.constructor);
   assertSame(C, (new C).__proto__.constructor);
-  assertEquals(1, C.length);
+  assertEquals(0, C.length);
 }
 TestConstructor(Set);
 TestConstructor(Map);
 TestConstructor(WeakMap);
 TestConstructor(WeakSet);
 
 
 // Test the Set, Map, WeakMap and WeakSet global properties themselves.
 function TestDescriptor(global, C) {
   assertEquals({
@@ skipping 1107 matching lines @@
   assertEquals(adderName + 'iterator', log);
 
   Object.defineProperty(ctor.prototype, adderName, {
     value: adderFunction
   });
 }
 TestConstructorOrderOfAdderIterator(Map, 'set');
 TestConstructorOrderOfAdderIterator(Set, 'add');
 TestConstructorOrderOfAdderIterator(WeakMap, 'set');
 TestConstructorOrderOfAdderIterator(WeakSet, 'add');