Fixs bug in notifying clients about hierarchy changes

services/ui/public/interfaces/window_tree.mojom

 // Copyright 2014 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 "cc/ipc/surface_id.mojom";
 import "cc/ipc/surface_sequence.mojom";
 import "cc/ipc/mojo_compositor_frame_sink.mojom";
 import "services/ui/public/interfaces/cursor.mojom";
@@ skipping 339 matching lines @@
 
   OnTransientWindowAdded(uint32 window_id,
                          uint32 transient_window_id);
 
   OnTransientWindowRemoved(uint32 window_id,
                            uint32 transient_window_id);
 
   // Invoked when a change is done to the hierarchy. A value of 0 is used to
   // identify a null window. For example, if the old_parent is NULL, 0 is
   // supplied.
-  // |windows| contains any windows that the client has not been told about.
+  // If |window| was not visible to this client, but is visible now because
+  // |new_parent| is visible to this client, then |windows| contains details
+  // about |window|, and all its descendants. |windows| includes any windows
+  // that client may already know about, but did not know the parent because
+  // the parent was previously not visible to this client.
   // This is not sent for hierarchy changes of windows not known to this client
   // or not attached to the tree.
   OnWindowHierarchyChanged(uint32 window,
                            uint32 old_parent,
                            uint32 new_parent,
                            array<WindowData> windows);
 
   // Invoked when the order of windows within a parent changes.
   OnWindowReordered(uint32 window_id,
                     uint32 relative_window_id,
@@ skipping 121 matching lines @@
   // See description of WindowManager for details.
   GetWindowManager(associated WindowManager& internal);
 };
 
 // Mus provides this interface as a way for clients to connect and obtain a
 // WindowTree handle with a supplied WindowTreeClient handle. The
 // WindowTreeClient has no roots, use NewTopLevelWindow() to create one.
 interface WindowTreeFactory {
   CreateWindowTree(WindowTree& tree_request, WindowTreeClient client);
 };