Work around https://bugs.freedesktop.org/show_bug.cgi?id=4320, which used

Work around https://bugs.freedesktop.org/show_bug.cgi?id=4320, which used

2006-02-03  Federico Mena Quintero  <federico@ximian.com>

	Work around https://bugs.freedesktop.org/show_bug.cgi?id=4320,
	which used to be our own
	http://bugzilla.gnome.org/show_bug.cgi?id=314616.  If one uses a
	pixmap for a pattern in Cairo, and sets the pattern to
	CAIRO_EXTEND_REPEAT; and if the destination surface is also a
	pixmap, Cairo does a slow copy instead of using XCopyArea().  So,
	we use the same code that we used in GTK+ 2.6 (pre-cairo), by
	filling the double-buffer pixmap with a tiled GC and
	XFillRectangle().

	* gdk/gdkwindow.c (BackingRectMethod): New structure with a
	cairo_t and a GdkGC field.  Depending on which of these fields
	gets filled in, we'll use Cairo or GDK to clear the double-buffer
	pixmap when painting a window.
	(setup_backing_rect_method): Fill a BackingRectMethod as
	appropriate, depending on the window's configuration and our
	knowledge of whether Cairo is fast or slow when doing repeating
	patterns.
	(gdk_window_clear_backing_rect): Call
	setup_backing_rect_method().  Depending on what it returns, use
	Cairo to clear the double-buffer pixmap, or plain GDK.