mus: Changes SetDisplayRoot() to create actual display

services/ui/public/interfaces/window_manager_constants.mojom

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 module ui.mojom;
 
 import "ui/display/mojo/display.mojom";
 import "ui/gfx/geometry/mojo/geometry.mojom";
 
 enum WindowManagerErrorCode {
@@ skipping 47 matching lines @@
   PANEL,
   WINDOW_FRAMELESS,
   CONTROL,
   POPUP,
   MENU,
   TOOLTIP,
   BUBBLE,
   DRAG,
   UNKNOWN,
 };
+
+// Used when the window manager explicitly adds a new display.
+struct WmViewportMetrics {
+  gfx.mojom.Rect bounds_in_pixels;
+  float device_scale_factor;
+  float ui_scale_factor;
+};