Makes WindowTree::DeleteWindow() unembed for roots

services/ui/public/interfaces/window_tree.mojom

Index: services/ui/public/interfaces/window_tree.mojom
diff --git a/services/ui/public/interfaces/window_tree.mojom b/services/ui/public/interfaces/window_tree.mojom
index d7bbd53256872b458e9ecc92fcc7981ada84ee7b..6d4782528b725a5ea7beb1088809b7f37f3846d0 100644
--- a/services/ui/public/interfaces/window_tree.mojom
+++ b/services/ui/public/interfaces/window_tree.mojom
@@ -65,7 +65,10 @@ interface WindowTree {
 
   // Deletes a window. This does not recurse. No hierarchy change notifications
   // are sent as a result of this. Only the connection that created the window
-  // can delete it.
+  // can delete it. DeleteWindow() may also be used to remove a window as an
+  // embed root from the client. When DeleteWindow() is used to remove an embed
+  // root, the client no longer has access to the embed root. The embedder of
+  // the root is notified of the change via OnEmbeddedAppDisconnected().
   DeleteWindow(uint32 change_id, uint32 window_id);
 
   // Requests input event capture for the given |window_id|. Capture is only