[Heap] Fix comparing against new space top pointer

test/mjsunit/regress/regress-619382.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: --expose-gc --always-opt
+
+(function __f_9() {
+})();
+function __f_16(ctor_desc) {
+  var __v_22 = 5;
+  var __v_25 = [];
+  gc(); gc(); gc();
+  for (var __v_18 = 0; __v_18 < __v_22; __v_18++) {
+    __v_25[__v_18] = ctor_desc.ctor.apply();
+  }
+}
+var __v_28 = [
+  {
+    ctor: function(__v_27) { return {a: __v_27}; },
+    args: function() { return [1.5 + __v_18]; }  },
+  {
+    ctor: function(__v_27) { var __v_21 = []; __v_21[1] = __v_27; __v_21[200000] = __v_27; return __v_21; },
+    args: function() { return [1.5 + __v_18]; }  },
+  {
+    ctor: function() {
+    }  }
+];
+var __v_26 = [
+  {
+  }];
+  __v_26.forEach(function(__v_16) {
+    __v_28.forEach(function(ctor) {
+      __f_16(ctor);
+    });
+  });