[proxies] Make Array.isArray respect proxies.

test/mjsunit/array-isarray.js

Index: test/mjsunit/array-isarray.js
diff --git a/test/mjsunit/array-isarray.js b/test/mjsunit/array-isarray.js
new file mode 100644
index 0000000000000000000000000000000000000000..a21b1e1e7dd53a7f279ff57792eacc8fb066cafa
--- /dev/null
+++ b/test/mjsunit/array-isarray.js
@@ -0,0 +1,16 @@
+// Copyright 2015 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: --harmony-proxies
+
+
+assertTrue(Array.isArray([]));
+assertFalse(Array.isArray({}));
+assertFalse(Array.isArray(null));
+
+assertTrue(Array.isArray(new Proxy([], {})));
+assertFalse(Array.isArray(new Proxy({}, {})));
+
+assertTrue(Array.isArray(new Proxy(new Proxy([], {}), {})));
+assertFalse(Array.isArray(new Proxy(new Proxy({}, {}), {})));