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

Source/core/xmlhttprequest/XMLHttpRequest.cpp

Index: Source/core/xmlhttprequest/XMLHttpRequest.cpp
diff --git a/Source/core/xmlhttprequest/XMLHttpRequest.cpp b/Source/core/xmlhttprequest/XMLHttpRequest.cpp
index f2ee9b1735e721ece197342204a99c54fc5c6740..36614aa269ae93774d50e0ecad1d38cb6a2d881e 100644
--- a/Source/core/xmlhttprequest/XMLHttpRequest.cpp
+++ b/Source/core/xmlhttprequest/XMLHttpRequest.cpp
@@ -144,17 +144,17 @@ public:
     }
 
     // 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();
     }