Rename visible_units.h to VisibleUnits.h in WebCore.vcxproj.filters
<http://webkit.org/b/111426>

* WebCore.vcxproj/WebCore.vcxproj.filters: Rename visible_units.h
to VisibleUnits.h and re-sort.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@145078 268f45cc-cd09-0410-ab3c-d52691b4dbfc