Added UseCounter for XML external DTD.

Source/core/xml/parser/XMLDocumentParser.cpp

 /*
  * Copyright (C) 2000 Peter Kelly (pmk@post.com)
  * Copyright (C) 2005, 2006, 2008, 2014 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2007 Samuel Weinig (sam@webkit.org)
  * Copyright (C) 2008 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2008 Holger Hans Peter Freyther
  * Copyright (C) 2008 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  *
  * This library is free software; you can redistribute it and/or
@@ skipping 639 matching lines @@
                 finalURL = resource->response().url();
             }
         }
     }
 
     // We have to check the URL again after the load to catch redirects.
     // See <https://bugs.webkit.org/show_bug.cgi?id=21963>.
     if (!shouldAllowExternalLoad(finalURL))
         return &globalDescriptor;
 
+    UseCounter::count(XMLDocumentParserScope::currentFetcher->document(), UseCounter::XMLExternalResourceLoad);
+
     return new SharedBufferReader(data);
 }
 
 static int readFunc(void* context, char* buffer, int len)
 {
     // Do 0-byte reads in case of a null descriptor
     if (context == &globalDescriptor)
         return 0;
 
     SharedBufferReader* data = static_cast<SharedBufferReader*>(context);
@@ skipping 965 matching lines @@
     sax.initialized = XML_SAX2_MAGIC;
     RefPtr<XMLParserContext> parser = XMLParserContext::createStringParser(&sax, &state);
     String parseString = "<?xml version=\"1.0\"?><attrs " + string + " />";
     parseChunk(parser->context(), parseString);
     finishParsing(parser->context());
     attrsOK = state.gotAttributes;
     return state.attributes;
 }
 
 } // namespace blink