Fix modeline to match file type. Bug 251968, patch by Andreas Lange

<anlan@ida.liu.se>, r+sr=bzbarsky

embedding/browser/powerplant/source/CTextInputEventHandling.cpp

@@ -1,4 +1,4 @@
-/* -*- Mode: IDL; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
  *
  * ***** BEGIN LICENSE BLOCK *****
  * Version: MPL 1.1/GPL 2.0/LGPL 2.1