st: Trigger theme updates on resolution changes

Commit de8a66d4ce removed our own DPI handling for the one found
it Clutter, but broke resolution updates at runtime (for instance
when setting the "Large Text" option in Universal Access).

https://bugzilla.gnome.org/show_bug.cgi?id=677975

src/st/st-theme-context.c

@@ -52,6 +52,7 @@ G_DEFINE_TYPE (StThemeContext, st_theme_context, G_TYPE_OBJECT)
 
 static void on_icon_theme_changed (StTextureCache *cache,
                                    StThemeContext *context);
+static void st_theme_context_changed (StThemeContext *context);
 
 static void
 st_theme_context_finalize (GObject *object)
@@ -61,6 +62,9 @@ st_theme_context_finalize (GObject *object)
   g_signal_handlers_disconnect_by_func (st_texture_cache_get_default (),
                                        (gpointer) on_icon_theme_changed,
                                        context);
+  g_signal_handlers_disconnect_by_func (clutter_get_default_backend (),
+                                        (gpointer) st_theme_context_changed,
+                                        context);
 
   if (context->root_node)
     g_object_unref (context->root_node);
@@ -97,6 +101,10 @@ st_theme_context_init (StThemeContext *context)
                     "icon-theme-changed",
                     G_CALLBACK (on_icon_theme_changed),
                     context);
+  g_signal_connect_swapped (clutter_get_default_backend (),
+                            "resolution-changed",
+                            G_CALLBACK (st_theme_context_changed),
+                            context);
 }
 
 /**