[Quota] Disable requestQuota operation on non-Document context

Source/modules/quota/StorageQuotaClient.cpp

 /*
  * Copyright (C) 2014 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 25 matching lines @@
 
 namespace WebCore {
 
 const char* StorageQuotaClient::supplementName()
 {
     return "StorageQuotaClient";
 }
 
 StorageQuotaClient* StorageQuotaClient::from(ExecutionContext* context)
 {
+    if (!context->isDocument())
+        return 0;
     return static_cast<StorageQuotaClient*>(WillBeHeapSupplement<Page>::from(toDocument(context)->page(), supplementName()));
 }
 
 void provideStorageQuotaClientTo(Page& page, PassOwnPtrWillBeRawPtr<StorageQuotaClient> client)
 {
     page.provideSupplement(StorageQuotaClient::supplementName(), client);
 }
 
 } // namespace WebCore