Remove unnecessary check in StoreProxy

Bug: v8:6560, chromium:761639
Change-Id: Idf546f53b20387670e42187692e702ba5e9eab73
Reviewed-on: https://chromium-review.googlesource.com/647550Reviewed-by: Igor Sheludko <ishell@chromium.org>
Commit-Queue: Maya Lekova <mslekova@google.com>
Cr-Commit-Position: refs/heads/master@{#47820}

src/ic/ic.cc

@@ -1678,7 +1678,6 @@ Handle<Object> StoreIC::StoreProxy(Handle<Map> receiver_map,
       GetPrototypeCheckCount(isolate(), receiver_map, proxy, name);
 
   DCHECK_LE(0, checks_count);
-  DCHECK(!receiver_map->IsJSGlobalObjectMap());
 
   Handle<Object> validity_cell =
       Map::GetOrCreatePrototypeChainValidityCell(receiver_map, isolate());

test/mjsunit/regress/regress-761639.js

+// Copyright 2017 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.
+
+// Regression test for hitting a DCHECK in StoreProxy.
+
+
+for (var i = 0; i < 10; i++) {
+  __proto__ = new Proxy({}, { getPrototypeOf() { } });
+}