Adds ability for WindowManager to create display roots

services/ui/ws/display.h

Index: services/ui/ws/display.h
diff --git a/services/ui/ws/display.h b/services/ui/ws/display.h
index 354b52e3ec0854cb6109e2fae69d72ed3f4e4ce6..9bdbcb701ed377bae0fcee290f89f8494db9b989 100644
--- a/services/ui/ws/display.h
+++ b/services/ui/ws/display.h
@@ -50,8 +50,7 @@ class DisplayTestApi;
 
 // Displays manages the state associated with a single display. Display has a
 // single root window whose children are the roots for a per-user
-// WindowManager. Display is configured in two distinct
-// ways:
+// WindowManager. Display is configured in two distinct ways:
 // . with a DisplayBinding. In this mode there is only ever one WindowManager
 //   for the display, which comes from the client that created the
 //   Display.
@@ -146,6 +145,10 @@ class Display : public PlatformDisplayDelegate,
   // Called just before |tree| is destroyed.
   void OnWillDestroyTree(WindowTree* tree);
 
+  // Removes |display_root| from internal maps. This called prior to
+  // |display_root| being destroyed.
+  void RemoveWindowManagerDisplayRoot(WindowManagerDisplayRoot* display_root);
+
   void UpdateNativeCursor(mojom::CursorType cursor_id);
 
   // mojom::WindowTreeHost: