Update V8 to r3431 as required by WebKit r51976.

Change-Id: I567392c3f8c0a0d5201a4249611ac4ccf468cd5b
diff --git a/test/mjsunit/mjsunit.js b/test/mjsunit/mjsunit.js
index 1fb3f02..8ced011 100644
--- a/test/mjsunit/mjsunit.js
+++ b/test/mjsunit/mjsunit.js
@@ -75,6 +75,9 @@
   if (typeof a == "number" && typeof b == "number" && isNaN(a) && isNaN(b)) {
     return true;
   }
+  if (a.constructor === RegExp || b.constructor === RegExp) {
+    return (a.constructor === b.constructor) && (a.toString === b.toString);
+  }
   if ((typeof a) !== 'object' || (typeof b) !== 'object' ||
       (a === null) || (b === null))
     return false;