[GTK][WK2] Update ContextMenu Download API
https://bugs.webkit.org/show_bug.cgi?id=120763

Patch by Brian Holt <brian.holt@samsung.com> on 2013-09-09
Reviewed by Carlos Garcia Campos.

Mark the new Download items in the Context Menu with the Since
tag, and include a unit test for Context Menu audio.

* UIProcess/API/gtk/WebKitContextMenuActions.h:
* UIProcess/API/gtk/tests/TestContextMenu.cpp:
(testContextMenuDefaultMenu):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@155345 268f45cc-cd09-0410-ab3c-d52691b4dbfc