Fix a bug in for/in iteration of arguments objects.

test/mjsunit/regress/regress-1531.js

Index: test/mjsunit/regress/regress-1531.js
diff --git a/test/mjsunit/regress/regress-1531.js b/test/mjsunit/regress/regress-1531.js
new file mode 100644
index 0000000000000000000000000000000000000000..6368e305e119864786c0a4d0a3bd15c43debd5a0
--- /dev/null
+++ b/test/mjsunit/regress/regress-1531.js
@@ -0,0 +1,49 @@
+// Copyright 2011 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
+//       copyright notice, this list of conditions and the following
+//       disclaimer in the documentation and/or other materials provided
+//       with the distribution.
+//     * Neither the name of Google Inc. nor the names of its
+//       contributors may be used to endorse or promote products derived
+//       from this software without specific prior written permission.
+//
+// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+// "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+// LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+// A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+// OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+// SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+// LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+// OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+// Regression test for computing elements keys of arguments object.  Should
+// not crash or assert.
+function test(x) {
+  arguments[10] = 0;
+  var arr = [];
+  for (var p in arguments) arr.push(p);
+  return arr;
+}
+assertEquals(["0", "10"], test(0));
+
+// Regression test for lookup after delete of a dictionary-mode arguments
+// backing store.  Should not crash or assert.
+function test1(x, y, z) {
+  // Put into dictionary mode.
+  arguments.__defineSetter__("5", function () { return 0; });
+  // Delete a property from the dictionary.
+  delete arguments[5];
+  // Look up a property in the dictionary.
+  return arguments[2];
+}
+
+assertEquals(void 0, test1(0));