Fix virtual/override/final usage in Source/core/{fetch,loader,streams,xmlhttprequest}/.

Source/core/xmlhttprequest/XMLHttpRequest.cpp

 /*
  *  Copyright (C) 2004, 2006, 2008 Apple Inc. All rights reserved.
  *  Copyright (C) 2005-2007 Alexey Proskuryakov <ap@webkit.org>
  *  Copyright (C) 2007, 2008 Julien Chaffraix <jchaffraix@webkit.org>
  *  Copyright (C) 2008, 2011 Google Inc. All rights reserved.
  *  Copyright (C) 2012 Intel Corporation
  *
  *  This library is free software; you can redistribute it and/or
  *  modify it under the terms of the GNU Lesser General Public
  *  License as published by the Free Software Foundation; either
@@ skipping 126 matching lines @@
 } // namespace
 
 class XMLHttpRequest::BlobLoader final : public GarbageCollectedFinalized<XMLHttpRequest::BlobLoader>, public FileReaderLoaderClient {
 public:
     static BlobLoader* create(XMLHttpRequest* xhr, PassRefPtr<BlobDataHandle> handle)
     {
         return new BlobLoader(xhr, handle);
     }
 
     // FileReaderLoaderClient functions.
-    virtual void didStartLoading() override { }
-    virtual void didReceiveDataForClient(const char* data, unsigned length) override
+    void didStartLoading() override {}
+    void didReceiveDataForClient(const char* data, unsigned length) override
     {
         ASSERT(length <= INT_MAX);
         m_xhr->didReceiveData(data, length);
     }
-    virtual void didFinishLoading() override
+    void didFinishLoading() override
     {
         m_xhr->didFinishLoadingFromBlob();
     }
-    virtual void didFail(FileError::ErrorCode error) override
+    void didFail(FileError::ErrorCode error) override
     {
         m_xhr->didFailLoadingFromBlob();
     }
 
     void cancel()
     {
         m_loader.cancel();
     }
 
     DEFINE_INLINE_TRACE()
@@ skipping 1497 matching lines @@
     visitor->trace(m_responseDocumentParser);
     visitor->trace(m_progressEventThrottle);
     visitor->trace(m_upload);
     visitor->trace(m_blobLoader);
     XMLHttpRequestEventTarget::trace(visitor);
     DocumentParserClient::trace(visitor);
     ActiveDOMObject::trace(visitor);
 }
 
 } // namespace blink