Log Message:
Update wip/webkit-gtk to 2.8.1.

Changes:
o Handle keep-alive connections in GStreamer HTTP source element.
o Fix a crash in DOMObjectCache when a wrapped object owned by the cache is
  unreffed by the user.
o Fix rendering of drag and drop icon.
o Fix the build with REDIRECTED_XCOMPOSITE_WINDOW disabled in X11 platform.
o Fix the build with Wayland target enabled.
o Fix the build for HPPA.