Bug 1607984 - P3. Fix leak in nsDSURIContentListener. r=smaug

If we were to open the window to close it immediately; we would leak a nsHtml5Parser object.

Differential Revision: https://phabricator.services.mozilla.com/D70000

docshell/base/nsDSURIContentListener.cpp

@@ -195,6 +195,7 @@ nsDSURIContentListener::DoContent(const nsACString& aContentType,
 
   if (NS_FAILED(rv)) {
     // we don't know how to handle the content
+    nsCOMPtr<nsIStreamListener> forget = dont_AddRef(*aContentHandler);
     *aContentHandler = nullptr;
     return rv;
   }