Avoid built-ins in `Date.prototype.toISOString`

test/mjsunit/date.js

Index: test/mjsunit/date.js
diff --git a/test/mjsunit/date.js b/test/mjsunit/date.js
index 3d72032ab81cbfb8b701a7e7b57d7a60e32a825b..0aadfdedcddd0df33365f7029deeef6920137941 100644
--- a/test/mjsunit/date.js
+++ b/test/mjsunit/date.js
@@ -340,3 +340,12 @@ date.getYear();
 %OptimizeFunctionOnNextCall(Date.prototype.getYear);
 assertThrows(function() { Date.prototype.getYear.call(""); }, TypeError);
 assertUnoptimized(Date.prototype.getYear);
+
+delete Date.prototype.getUTCFullYear;
+delete Date.prototype.getUTCMonth;
+delete Date.prototype.getUTCDate;
+delete Date.prototype.getUTCHours;
+delete Date.prototype.getUTCMinutes;
+delete Date.prototype.getUTCSeconds;
+delete Date.prototype.getUTCMilliseconds;
+date.toISOString();