chromeos: Makes mushrome use simplified display management

ash/mus/standalone/manifest.json

+{
+  "name": "standalone_ash",
+  "display_name": "Standalone (testing) Ash Window Manager and Shell",
+  "interface_provider_specs": {
+    "service_manager:connector": {
+      "provides": {
+        // Modifications here should correspond with changes to
+        // chrome_content_browser_manifest_overlay.json.
+        "ash": [
+          "app_list::mojom::AppList",
+          "ash::mojom::AcceleratorController",
+          "ash::mojom::CastConfig",
+          "ash::mojom::LocaleNotificationController",
+          "ash::mojom::MediaController",
+          "ash::mojom::NewWindowController",
+          "ash::mojom::SessionController",
+          "ash::mojom::ShelfController",
+          "ash::mojom::ShutdownController",
+          "ash::mojom::SystemTray",
+          "ash::mojom::TouchViewManager",
+          "ash::mojom::VpnList",
+          "ash::mojom::WallpaperController"
+        ],
+        "mus:window_manager": [ "ui::mojom::AcceleratorRegistrar" ]
+      },
+      "requires": {
+        "*": [ "accessibility", "app" ],
+        "preferences_forwarder": [ "pref_client" ],
+        "ui": [ "display_test", "window_manager" ],
+        "touch_hud": [ "mash:launchable" ]
+      }
+    }
+  }
+}