webkitgtk: Use-after-free issue in accessibility/AXObjectCache.cpp

WebKitGTK through 2.26.4 and WPE WebKit through 2.26.4 which are the versions right before 2.28.0 contains a memory corruption issue use-after-free that may lead to arbitrary code execution. This issue has been fixed in 2.28.0 with improved memory handling...