Bug 38648

After some investigation while working for fixing bug 31018, I found that the AtkObject* returned by AccessibilityController::rootElement() -in AccessibilityControllerGtk.cpp- is *not a valid AtkObject* at all (ATK_ROLE_INVALID), which makes impossible to later access to its only child and therefore any AccessibleUIElement associated to the DOM's elements. As a consecuence of this, it was not possible to implement the isSelected() method in DRT to make the accessibility/aria-controls-with-tabs.html test success, as it was not possible to access to any AccessibleUIElement in the DOM starting from the root element. After some investigation I found the problem was that the GAIL Gtk module was not being loaded along with the execution of DRT (even if the environment variable was already set), and that's the reason behind those AtkObjects returned by rootElement() not being valid. Therefore, we need to make sure GAIL is always loaded with DRT if we want this kind of a11y tests (using the AccessibleUIElements starting from the root element) work properly. As side note: it seems that some a11y apps like Orca and Accerciser manually make sure the GTK_MODULES envvar is properly loaded along with their executions, so perhaps that's the way to go here, providing it would only affect to the GTK implementation of the DRT.