Fix build warning after r147022
https://bugs.webkit.org/show_bug.cgi?id=113567

Patch by KwangYong Choi <ky0.choi@samsung.com> on 2013-03-29
Reviewed by Kentaro Hara.

Use UNUSED_PARAM macro to fix -Wunused-parameter build warning.
No new tests, no change on behavior.

* page/EventHandler.cpp:
(WebCore::expandSelectionToRespectUserSelectAll):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@147210 268f45cc-cd09-0410-ab3c-d52691b4dbfc