Bug 577130 xmlparser should tell channels that it expects the content to be xml

r=peterv

parser/htmlparser/src/nsExpatDriver.cpp

@@ -799,14 +799,17 @@ nsExpatDriver::OpenInputStreamFromExternalDTD(const PRUnichar* aFPIStr,
     return NS_ERROR_CONTENT_BLOCKED;
   }
 
-  rv = NS_OpenURI(aStream, uri);
-
   nsCAutoString absURL;
   uri->GetSpec(absURL);
 
   CopyUTF8toUTF16(absURL, aAbsURL);
 
-  return rv;
+  nsCOMPtr<nsIChannel> channel;
+  rv = NS_NewChannel(getter_AddRefs(channel), uri);
+  NS_ENSURE_SUCCESS(rv, rv);
+
+  channel->SetContentType(NS_LITERAL_CSTRING("application/xml"));
+  return channel->Open(aStream);
 }
 
 static nsresult