Prevent a crash if the window was deleted while in a drag runloop

ash/wm/toplevel_window_event_handler.cc

 // Copyright (c) 2012 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 "ash/wm/toplevel_window_event_handler.h"
 
 #include "ash/aura/wm_window_aura.h"
 #include "ash/common/wm/window_state.h"
 #include "ash/shell.h"
 #include "ash/wm/window_state_aura.h"
 #include "base/message_loop/message_loop.h"
 #include "base/run_loop.h"
 #include "ui/aura/client/cursor_client.h"
 #include "ui/aura/env.h"
 #include "ui/aura/window.h"
 #include "ui/aura/window_event_dispatcher.h"
+#include "ui/aura/window_tracker.h"
 #include "ui/aura/window_tree_host.h"
 #include "ui/base/cursor/cursor.h"
 #include "ui/base/hit_test.h"
 #include "ui/events/event.h"
 #include "ui/events/event_utils.h"
 #include "ui/events/gestures/gesture_recognizer.h"
 
 namespace ash {
 
 ToplevelWindowEventHandler::ToplevelWindowEventHandler(WmShell* shell)
@@ skipping 60 matching lines @@
   base::WeakPtr<ToplevelWindowEventHandler> weak_ptr(
       weak_factory_.GetWeakPtr());
   base::MessageLoop* loop = base::MessageLoop::current();
   base::MessageLoop::ScopedNestableTaskAllower allow_nested(loop);
 
   // Disable window position auto management while dragging and restore it
   // aftrewards.
   wm::WindowState* window_state = wm::GetWindowState(source);
   const bool window_position_managed = window_state->window_position_managed();
   window_state->set_window_position_managed(false);
+  aura::WindowTracker tracker({source});
 
   run_loop.Run();
 
   if (!weak_ptr)
     return aura::client::MOVE_CANCELED;
 
-  window_state->set_window_position_managed(window_position_managed);
+  // Make sure the window hasn't been deleted.
+  if (tracker.Contains(source))
+    window_state->set_window_position_managed(window_position_managed);
 
   in_move_loop_ = false;
   return result == wm::WmToplevelWindowEventHandler::DragResult::SUCCESS
              ? aura::client::MOVE_SUCCESSFUL
              : aura::client::MOVE_CANCELED;
 }
 
 void ToplevelWindowEventHandler::EndMoveLoop() {
   if (in_move_loop_)
     wm_toplevel_window_event_handler_.RevertDrag();
 }
 
 void ToplevelWindowEventHandler::OnDragCompleted(
     wm::WmToplevelWindowEventHandler::DragResult* result_return_value,
     base::RunLoop* run_loop,
     wm::WmToplevelWindowEventHandler::DragResult result) {
   *result_return_value = result;
   run_loop->Quit();
 }
 
 }  // namespace ash