This enables tracking of ARGB values for image masks, since some machines do 
not use ARGB values. 
See Mozilla bug #716462 - Performance regression with xBGR visual and no 
RENDER extension. 
We would like to try to get this upstream in the future. 

--- mozilla-esr31/gfx/cairo/cairo/src/cairo-xlib-surface.c.orig	2015-06-04 17:42:51.419088049 -0700
+++ mozilla-esr31/gfx/cairo/cairo/src/cairo-xlib-surface.c	2015-06-04 17:42:51.424665839 -0700
@@ -2325,6 +2325,7 @@
 			   cairo_region_t *clip_region)
 {
     cairo_image_surface_t *image;
+    cairo_format_masks_t image_masks;
     cairo_rectangle_int_t extents;
     cairo_status_t status;
     int tx, ty;
@@ -2341,6 +2342,16 @@
 	    (image->base.content & CAIRO_CONTENT_ALPHA) == 0)))
 	return CAIRO_INT_STATUS_UNSUPPORTED;
 
+    if (image->base.backend->type == CAIRO_SURFACE_TYPE_IMAGE) {
+	if (_pixman_format_to_masks (image->pixman_format, &image_masks)) {
+	    if (! ((image_masks.alpha_mask == surface->a_mask || surface->a_mask == 0) &&
+		   (image_masks.red_mask   == surface->r_mask || surface->r_mask == 0) &&
+		   (image_masks.green_mask == surface->g_mask || surface->g_mask == 0) &&
+		   (image_masks.blue_mask  == surface->b_mask || surface->b_mask == 0)))
+		return CAIRO_INT_STATUS_UNSUPPORTED;
+	}
+    }
+
     if (image->base.backend->type != CAIRO_SURFACE_TYPE_IMAGE) {
 	if (image->base.backend->type == CAIRO_INTERNAL_SURFACE_TYPE_SNAPSHOT) {
 	    image = (cairo_image_surface_t *) ((cairo_surface_snapshot_t *) image)->target;