Reviewed by Jan Alonzo.

        https://bugs.webkit.org/show_bug.cgi?id=25897
        [Gtk] Extraneous object of ROLE_PANEL in hierarchy for entries

        Expands upon the new funtionality which allows platforms to indicate
        that a particular object should not be ignored, so that they can
        specify that an object should be ignored or that it should be left up
        to the default handling to decide.

        * accessibility/AccessibilityObject.h:
        * accessibility/chromium/AccessibilityObjectChromium.cpp:
        * accessibility/gtk/AccessibilityObjectAtk.cpp:
        * accessibility/mac/AccessibilityObjectMac.mm:
        * accessibility/qt/AccessibilityObjectQt.cpp:
        * accessibility/win/AccessibilityObjectWin.cpp:
        * accessibility/wx/AccessibilityObjectWx.cpp:
        (AccessibilityObject::accessibilityPlatformIncludesObject):
        * accessibility/AccessibilityRenderObject.cpp:
        (AccessibilityRenderObject::accessibilityIsIgnored):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@50220 268f45cc-cd09-0410-ab3c-d52691b4dbfc