Build break when disabled ACCESSIBILITY since r162986
https://bugs.webkit.org/show_bug.cgi?id=128880

Unreviewed build fix.


* WebKitTestRunner/InjectedBundle/AccessibilityUIElement.cpp:
Added dummy implementations for newly added methods.
(WTR::AccessibilityUIElement::rowHeaders):
(WTR::AccessibilityUIElement::columnHeaders):
(WTR::AccessibilityUIElement::ariaControlsElementAtIndex):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@164189 268f45cc-cd09-0410-ab3c-d52691b4dbfc