[BlackBerry] Add dummy implementations of DragData::droppedFileSystemId()
https://bugs.webkit.org/show_bug.cgi?id=114861

Patch by Alberto Garcia <agarcia@igalia.com> on 2013-04-22
Reviewed by Carlos Garcia Campos.

* platform/blackberry/DragDataBlackBerry.cpp:
(WebCore):
(WebCore::DragData::droppedFileSystemId):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@148870 268f45cc-cd09-0410-ab3c-d52691b4dbfc