ES6: Fix GetIterator

After further spec reading it turns out that we should not do ToObject
on the iterable.

BUG=None
LOG=N
R=adamk

Review URL: https://codereview.chromium.org/941313003

Cr-Commit-Position: refs/heads/master@{#26786}

src/v8natives.js

@@ -1883,7 +1883,7 @@ SetUpFunction();
 // 7.4.1 GetIterator ( obj, method )
 function GetIterator(obj, method) {
   if (IS_UNDEFINED(method)) {
-    method = ToObject(obj)[symbolIterator];
+    method = obj[symbolIterator];
   }
   if (!IS_SPEC_FUNCTION(method)) {
     throw MakeTypeError('not_iterable', [obj]);

test/mjsunit/es6/collections.js

@@ -1190,7 +1190,7 @@ function TestSetConstructorIterableValue(ctor) {
   // Strict mode is required to prevent implicit wrapping in the getter.
   Object.defineProperty(Number.prototype, Symbol.iterator, {
     get: function() {
-      assertEquals('object', typeof this);
+      assertEquals('number', typeof this);
       return function() {
         assertEquals('number', typeof this);
         return oneAndTwo.keys();
@@ -1381,7 +1381,7 @@ function TestMapConstructorIterableValue(ctor) {
   // Strict mode is required to prevent implicit wrapping in the getter.
   Object.defineProperty(Number.prototype, Symbol.iterator, {
     get: function() {
-      assertEquals('object', typeof this);
+      assertEquals('number', typeof this);
       return function() {
         assertEquals('number', typeof this);
         return oneAndTwo.entries();