Expand and split DisplayController mojom.

services/ui/manifest.json

 {
   "manifest_version":  1,
   "name": "service:ui",
   "display_name": "UI Service",
   "capabilities": {
     "provided": {
       // A collection of interfaces needed by a generic client of mus.
       // Additional interfaces may be requested a-la-carte.
       "app": [
         "ui::mojom::Clipboard",
@@ skipping 16 matching lines @@
         "ui::mojom::GpuService"
       ],
       "ui:ime_registrar": [
         "ui::mojom::IMERegistrar"
       ],
       "ui:user_access_manager": [
         "ui::mojom::UserAccessManager"
       ],
       "ui:window_manager": [
         "display::mojom::DisplayController",
+        "display::mojom::TestDisplayController",
         "ui::mojom::AccessibilityManager",
         "ui::mojom::WindowManagerWindowTreeFactory"
       ],
       "ui:window_tree_host_factory": [
         "ui::mojom::WindowTreeHostFactory"
       ]
     },
     "required": {
       "*": [ "app" ],
       "service:service_manager": [
         "service_manager:all_users",
         "service_manager:explicit_class"
       ],
       "service:ui": [ "ozone" ]
     }
   }
 }