https://bugs.webkit.org/show_bug.cgi?id=40193

Reviewed by Chris Fleizach.

Source/WebKit/gtk:

Add support for retrieving WebCore's AccessibilityObject's
helpText from the GTK DumpRenderTree.

* WebCoreSupport/DumpRenderTreeSupportGtk.cpp:
(DumpRenderTreeSupportGtk::accessibilityHelpText): Returns result
of calling to helpText() over the core accessibility object's.
* WebCoreSupport/DumpRenderTreeSupportGtk.h:

Tools:

* DumpRenderTree/gtk/AccessibilityUIElementGtk.cpp:
(AccessibilityUIElement::helpText): Implemented.

LayoutTests:

Unskip tests now passing.

* accessibility/aria-describedby-on-input-expected.txt: Moved from
LayoutTests/platform/mac/accessibility.
* platform/gtk/Skipped: Unskip tests.

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@104591 268f45cc-cd09-0410-ab3c-d52691b4dbfc