Current custom call generators cannot cope with the case when receiver is not a JSArray.

test/mjsunit/array-push.js

 // Copyright 2010 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
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@@ skipping 85 matching lines @@
     assertEquals(22, a.push(22));
     assertEquals(23, a.push(23));
     assertEquals(24, a.push(24));
     assertEquals(25, a.push(25));
     assertEquals(26, a.push(26));
     assertEquals(27, a.push(27));
     assertEquals(28, a.push(28));
     assertEquals(29, a.push(29));
   }
 })();
+
+// Test the case of not JSArray receiver.
+// Regression test for custom call generators, see issue 684.
+(function() {
+  var x = {__proto__: []};
+  for (var i = 0; i < 100; i++) {
+    x.push("a");
+    assertEquals(i + 1, x.length, i + 'th iteration');
+  }
+})();