[proxy] fixing harmony/proxy.js tests and improving error messages + some drive-by fixes

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

+// Copyright 2015 the V8 project authors. All rights reserved.

[dingxiangfei2009, 2015/12/12 01:27:01]

The file name has a typo

+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --harmony-proxies
+
+// Do not read out the prototype from a cross-realm object.
+var realm = Realm.create();
+
+__proto__ = { get foo() { print("+++++++++++++"); } };
+Realm.eval(realm, "Reflect.getPrototypeOf(Realm.global(0))");
+
+// 2-level indirection
+__proto__ = new Proxy({},
+  new Proxy({}, {
+    get() { assertUnreachable() }
+  })
+);
+Realm.eval(realm, "Realm.global(0) instanceof Object");