[heap] Don't consider mementos on pages below age mark

test/mjsunit/regress/regress-631050.js

 // Copyright 2016 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
+//
+// Flags: --gc-global --stress-runs=8
 
-// Flags: --allow-natives-syntax
-
-function foo() {
-  return [] | 0 && values[0] || false;
+function __f_3(x, expected) {
+  var __v_3 = [];
+  __v_3.length = x;
+  __f_3(true, 1);
 }
 
-%OptimizeFunctionOnNextCall(foo);
 try {
-  foo();
+  __f_3(2147483648, 2147483648);
 } catch (e) {}