Upgrade V8 to 5.1.281.57

Change-Id: Id981b686b4d587ac31697662eb98bb34be42ad90
diff --git a/test/mjsunit/harmony/sharedarraybuffer.js b/test/mjsunit/harmony/sharedarraybuffer.js
index 7f7f8fb..7bd4e5b 100644
--- a/test/mjsunit/harmony/sharedarraybuffer.js
+++ b/test/mjsunit/harmony/sharedarraybuffer.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: --harmony-sharedarraybuffer --harmony-tostring
+// Flags: --harmony-sharedarraybuffer
 
 
 // SharedArrayBuffer