Object.observe: avoid accessing acceptList properties more than once

test/mjsunit/regress/regress-3315.js

Index: test/mjsunit/regress/regress-3315.js
diff --git a/test/mjsunit/regress/regress-3315.js b/test/mjsunit/regress/regress-3315.js
new file mode 100644
index 0000000000000000000000000000000000000000..a1105e28488971dca2a930db92f22b8cde26866d
--- /dev/null
+++ b/test/mjsunit/regress/regress-3315.js
@@ -0,0 +1,26 @@
+// Copyright 2014 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.
+
+var indexZeroCallCount = 0;
+var indexOneCallCount = 0;
+var lengthCallCount = 0;
+var acceptList = {
+  get 0() {
+    indexZeroCallCount++;
+    return 'foo';
+  },
+  get 1() {
+    indexOneCallCount++;
+    return 'bar';
+  },
+  get length() {
+    lengthCallCount++;
+    return 1;
+  }
+};
+
+Object.observe({}, function(){}, acceptList);
+assertEquals(1, lengthCallCount);
+assertEquals(1, indexZeroCallCount);
+assertEquals(0, indexOneCallCount);