Snapshotted plug-in should use shadow root
https://bugs.webkit.org/show_bug.cgi?id=108284

Unreviewed GTK+ build fix.

* Source/autotools/symbols.filter: Export InlineBox symbols.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@142345 268f45cc-cd09-0410-ab3c-d52691b4dbfc