ES6: Make sure we do not store -0 as the key in Map/Set

src/collection.js

 // Copyright 2012 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.
 
 "use strict";
 
 // This file relies on the fact that the following declaration has been made
 // in runtime.js:
 // var $Array = global.Array;
 
@@ skipping 31 matching lines @@
     %_CallFunction(this, next.value, adder);
   }
 }
 
 
 function SetAddJS(key) {
   if (!IS_SET(this)) {
     throw MakeTypeError('incompatible_method_receiver',
                         ['Set.prototype.add', this]);
   }
+  // Normalize -0 to +0 as required by the spec.
+  // Even though we use SameValueZero as the comparison for the keys we don't
+  // want to ever store -0 as the key since the key is directly exposed when
+  // doing iteration.
+  if (key === 0) {
+    key = 0;
+  }
   return %SetAdd(this, key);
 }
 
 
 function SetHasJS(key) {
   if (!IS_SET(this)) {
     throw MakeTypeError('incompatible_method_receiver',
                         ['Set.prototype.has', this]);
   }
   return %SetHas(this, key);
@@ skipping 117 matching lines @@
   }
   return %MapGet(this, key);
 }
 
 
 function MapSetJS(key, value) {
   if (!IS_MAP(this)) {
     throw MakeTypeError('incompatible_method_receiver',
                         ['Map.prototype.set', this]);
   }
+  // Normalize -0 to +0 as required by the spec.
+  // Even though we use SameValueZero as the comparison for the keys we don't
+  // want to ever store -0 as the key since the key is directly exposed when
+  // doing iteration.
+  if (key === 0) {
+    key = 0;
+  }
   return %MapSet(this, key, value);
 }
 
 
 function MapHasJS(key) {
   if (!IS_MAP(this)) {
     throw MakeTypeError('incompatible_method_receiver',
                         ['Map.prototype.has', this]);
   }
   return %MapHas(this, key);
@@ skipping 64 matching lines @@
     "get", MapGetJS,
     "set", MapSetJS,
     "has", MapHasJS,
     "delete", MapDeleteJS,
     "clear", MapClearJS,
     "forEach", MapForEach
   ));
 }
 
 SetUpMap();