https://bugs.webkit.org/show_bug.cgi?id=121165

Reviewed by Martin Robinson.

This is analogous to the changes in r154728 and r154729 that enforce disabling accelerated compositing
under Wayland displays and made the RedirectedXCompositeWindow use in WebKit2 limited only to the X11 displays.

* WebCoreSupport/AcceleratedCompositingContextGL.cpp: Remove two unnecessary header includes that also
introduce symbols that conflict with the symbols defined in the X headers. Include the <gdk/gdkx.h> header
if the GTK+ dependency can provide it.
(WebKit::AcceleratedCompositingContext::initialize): Only set up the RedirectedXCompositeWindow instance
if running under an X11 display.
(WebKit::AcceleratedCompositingContext::renderLayersToWindow): The removal of the unnecessary header
inclusions also removed the std::max() injection into the global scope. Using std::max directly instead.
(WebKit::AcceleratedCompositingContext::scheduleLayerFlush): Ditto.
* webkit/webkitwebview.cpp:
(updateAcceleratedCompositingSetting): A helper function that ensures the accelerated compositing feature
stays disabled under Wayland displays. It also prints out a warning message the first time the user tries
to enable accelerated compositing under Wayland displays, telling that the feature is not supported and
will remain disabled.
(webkit_web_view_update_settings): Call updateAcceleratedCompositingSetting() to enable the feature if possible.
(webkit_web_view_settings_notify): Ditto.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@155619 268f45cc-cd09-0410-ab3c-d52691b4dbfc