Upgrade V8 to 5.1.281.57

Change-Id: Id981b686b4d587ac31697662eb98bb34be42ad90
diff --git a/test/mjsunit/es6/array-iterator.js b/test/mjsunit/es6/array-iterator.js
index 5fab0fb..d2d19b0 100644
--- a/test/mjsunit/es6/array-iterator.js
+++ b/test/mjsunit/es6/array-iterator.js
@@ -25,7 +25,7 @@
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
-// Flags: --allow-natives-syntax --harmony-tostring
+// Flags: --allow-natives-syntax
 
 
 var NONE = 0;
@@ -160,7 +160,7 @@
   assertArrayEquals(['next'],
       Object.getOwnPropertyNames(ArrayIteratorPrototype));
   assertHasOwnProperty(ArrayIteratorPrototype, 'next', DONT_ENUM);
-  assertHasOwnProperty(ArrayIteratorPrototype, Symbol.iterator, DONT_ENUM);
+  assertFalse(ArrayIteratorPrototype.hasOwnProperty(Symbol.iterator));
 
   assertEquals("[object Array Iterator]",
       Object.prototype.toString.call(iterator));