Handle modified displays in mustash.

services/ui/public/interfaces/window_manager.mojom

Index: services/ui/public/interfaces/window_manager.mojom
diff --git a/services/ui/public/interfaces/window_manager.mojom b/services/ui/public/interfaces/window_manager.mojom
index cc38b18c2bf3ec266bb6ae7a4af857f64a2188ad..80569d45c547444cf2af4e10e5fd3ec53519b48e 100644
--- a/services/ui/public/interfaces/window_manager.mojom
+++ b/services/ui/public/interfaces/window_manager.mojom
@@ -97,6 +97,10 @@ interface WindowManager {
   // this with the root.
   WmDisplayRemoved(int64 display_id);
 
+  // Called when a display is modified. The root of the specified display will
+  // be resized by the WindowServer after this.
+  WmDisplayModified(display.mojom.Display display);
+
   // When the WindowManager completes a request it must call back to
   // WindowManagerClient::WmResponse().
   WmSetBounds(uint32 change_id, uint32 window_id, gfx.mojom.Rect bounds);