shims: Use cairo PNG support instead of GDK

It is inferior, but at least doesn't print warnings on Travis due
to the lack of X server.

lib/gears/surface.lua

@@ -51,7 +51,13 @@ function surface.load_uncached_silently(_surface, default)
         if not pixbuf then
             return get_default(default), tostring(err)
         end
-        _surface = capi.awesome.pixbuf_to_surface(pixbuf._native)
+        _surface = capi.awesome.pixbuf_to_surface(pixbuf._native, _surface)
+
+        -- The shims implement load_image() to return a surface directly,
+        -- instead of a lightuserdatum.
+        if cairo.Surface:is_type_of(_surface) then
+            return _surface
+        end
     end
     -- Everything else gets forced into a surface
     return cairo.Surface(_surface, true)

luaa.c

@@ -284,6 +284,7 @@ luaA_sync(lua_State *L)
 /** Translate a GdkPixbuf to a cairo image surface..
  *
  * @param pixbuf The pixbuf as a light user datum.
+ * @param path The pixbuf origin path
  * @return A cairo surface as light user datum.
  * @function pixbuf_to_surface
  */

tests/examples/shims/awesome.lua

@@ -1,6 +1,4 @@
 local lgi       = require("lgi")
-local GdkPixbuf = lgi.GdkPixbuf
-local Gdk       = lgi.Gdk
 local gears_obj = require("gears.object")
 
 -- Emulate the C API classes. They differ from C API objects as connect_signal
@@ -48,27 +46,10 @@ awesome.startup = true
 function awesome.register_xproperty()
 end
 
-local init, surfaces = false, {}
+awesome.load_image = lgi.cairo.ImageSurface.create_from_png
 
-function awesome.load_image(file)
+function awesome.pixbuf_to_surface(_, path)
-    if not init then
+    return awesome.load_image(path)
-        Gdk.init{}
-        init = true
-    end
-
-    local _, width, height = GdkPixbuf.Pixbuf.get_file_info(file)
-
-    local pixbuf = GdkPixbuf.Pixbuf.new_from_file_at_size(file, width, height)
-
-    if not pixbuf then
-        return nil, "Could not load "..file
-    end
-
-    local s = Gdk.cairo_surface_create_from_pixbuf( pixbuf, 1, nil )
-
-    table.insert(surfaces, s)
-
-    return s._native, not s and "Could not load surface from "..file or nil, s
 end
 
 -- Always show deprecated messages