[GTK] Guard uses of RedirectedXCompositeWindow in WebKitWebViewBase with PLATFORM...

[GTK] Guard uses of RedirectedXCompositeWindow in WebKitWebViewBase with PLATFORM(X11)
https://bugs.webkit.org/show_bug.cgi?id=133871

Reviewed by Martin Robinson.

Guard uses of the RedirectedXCompositeWindow object in WebKitWebViewBase with the
PLATFORM(X11) build guard. This is required to properly support building the GTK
port only for the Wayland target.

* UIProcess/API/gtk/WebKitWebViewBase.cpp:
(webkitWebViewBaseConstructed):
(webkitWebViewRenderAcceleratedCompositingResults):
(resizeWebKitWebViewBaseFromAllocation):
(webkitWebViewBaseUpdatePreferences):
(webkitWebViewBaseCreateWebPage):

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@170887 268f45cc-cd09-0410-ab3c-d52691b4dbfc