Upgrade V8 to 5.1.281.57  DO NOT MERGE

FPIIM-449

Change-Id: Id981b686b4d587ac31697662eb98bb34be42ad90
(cherry picked from commit 3b9bc31999c9787eb726ecdbfd5796bfdec32a18)
diff --git a/test/mjsunit/compiler/regress-const.js b/test/mjsunit/compiler/regress-const.js
index 89b559c..5099c2f 100644
--- a/test/mjsunit/compiler/regress-const.js
+++ b/test/mjsunit/compiler/regress-const.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 --legacy-const
+// Flags: --allow-natives-syntax
 
 // Test const initialization and assignments.
 function f() {
@@ -38,7 +38,6 @@
 
 function g() {
   const x = 42;
-  x += 1;
   return x;
 }
 
@@ -50,7 +49,7 @@
 %OptimizeFunctionOnNextCall(f);
 %OptimizeFunctionOnNextCall(g);
 
-assertEquals(42, f());
+assertEquals(1, f());
 assertEquals(42, g());