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;