[proxies] fix access issue when having proxies on the prototype-chain of global objects.

test/mjsunit/harmony/proxies-cross-realm-exception.js

Index: test/mjsunit/harmony/proxies-cross-realm-exception.js
diff --git a/test/mjsunit/harmony/proxies-cross-realm-exception.js b/test/mjsunit/harmony/proxies-cross-realm-exception.js
new file mode 100644
index 0000000000000000000000000000000000000000..5530a60fed3f23d749cb2f867ebce7ccf204966e
--- /dev/null
+++ b/test/mjsunit/harmony/proxies-cross-realm-exception.js
@@ -0,0 +1,53 @@
+// 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 --harmony-reflect --allow-natives-syntax
+
+// Do not read out the prototype from a cross-realm object.
+var realm = Realm.create();
+
+__proto__ = {};
+assertEquals(null,
+  Realm.eval(realm, "3; Reflect.getPrototypeOf(Realm.global(0))"));
+assertFalse(Realm.eval(realm, "3; Realm.global(0) instanceof Object"));
+
+__proto__ = new Proxy({}, { getPrototypeOf() { assertUnreachable() } });
+assertEquals(null,
+    Realm.eval(realm, "1; Reflect.getPrototypeOf(Realm.global(0))"));
+assertFalse(Realm.eval(realm, "1; Realm.global(0) instanceof Object"));
+
+// Test that the instannceof check works in optimized code.
+var test = Realm.eval(realm,
+    "()=>{1.1; return Realm.global(0) instanceof Object; }");
+assertFalse(test());
+test();
+test();
+%OptimizeFunctionOnNextCall(test);
+assertFalse(test());
+
+__proto__ = {};
+__proto__ = new Proxy({}, { get(t, p, r) { assertUnreachable() } });
+assertEquals(null,
+    Realm.eval(realm, "2; Reflect.getPrototypeOf(Realm.global(0))"));
+assertFalse(Realm.eval(realm, "2; Realm.global(0) instanceof Object"));
+
+
+__proto__ = {};
+__proto__.__proto__ = new Proxy({}, {
+  getPrototypeOf() { assertUnreachable() }
+});
+assertEquals(null,
+  Realm.eval(realm, "4; Reflect.getPrototypeOf(Realm.global(0))"));
+assertFalse(Realm.eval(realm, "4; Realm.global(0) instanceof Object"));
+
+// 2-level proxy indirection
+__proto__ = {};
+__proto__ = new Proxy({},
+  new Proxy({}, {
+    get() { assertUnreachable() }
+  })
+);
+assertEquals(null,
+  Realm.eval(realm, "5; Reflect.getPrototypeOf(Realm.global(0))"));
+assertFalse(Realm.eval(realm, "5; Realm.global(0) instanceof Object"));