Fixes bug in handling restacking because of transients

ui/aura/mus/window_tree_client.cc

 // 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.
 
 #include "ui/aura/mus/window_tree_client.h"
 
 #include <stddef.h>
 
 #include <string>
 #include <utility>
@@ skipping 1532 matching lines @@
   }
   // The change originated from client code and needs to be sent to the server.
   DCHECK(tree_);
   WindowMus* child_mus = WindowMus::Get(transient_child);
   const uint32_t change_id =
       ScheduleInFlightChange(base::MakeUnique<CrashInFlightChange>(
           child_mus, ChangeType::REMOVE_TRANSIENT_WINDOW_FROM_PARENT));
   tree_->RemoveTransientWindowFromParent(change_id, child_mus->server_id());
 }
 
+void WindowTreeClient::OnWillRestackTransientChildAbove(Window* source,
+                                                        Window* window) {
+  DCHECK(source->parent());
+  DCHECK_EQ(source->parent(), window->parent());
+  WindowMus::Get(source->parent())
+      ->PrepareForTransientRestack(WindowMus::Get(window));
+}
+
+void WindowTreeClient::OnDidRestackTransientChildAbove(Window* source,
+                                                       Window* window) {
+  DCHECK(source->parent());
+  DCHECK_EQ(source->parent(), window->parent());
+  WindowMus::Get(source->parent())
+      ->OnTransientRestackDone(WindowMus::Get(window));
+}
+
 uint32_t WindowTreeClient::CreateChangeIdForDrag(WindowMus* window) {
   return ScheduleInFlightChange(
       base::MakeUnique<InFlightDragChange>(window, ChangeType::DRAG_LOOP));
 }
 
 uint32_t WindowTreeClient::CreateChangeIdForCapture(WindowMus* window) {
   return ScheduleInFlightChange(base::MakeUnique<InFlightCaptureChange>(
       this, capture_synchronizer_.get(), window));
 }
 
 uint32_t WindowTreeClient::CreateChangeIdForFocus(WindowMus* window) {
   return ScheduleInFlightChange(base::MakeUnique<InFlightFocusChange>(
       this, focus_synchronizer_.get(), window));
 }
 
 }  // namespace aura