Changes how window manager obtains WindowTree from mus

ash/mus/disconnected_app_handler.cc

 // Copyright 2016 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/mus/disconnected_app_handler.h"
 
+#include "ash/common/shell_window_ids.h"
+#include "ash/mus/bridge/wm_window_mus.h"
+
 namespace ash {
 namespace mus {
+namespace {
 
-DisconnectedAppHandler::DisconnectedAppHandler() {}
+bool IsContainer(::mus::Window* window) {
+  return WmWindowMus::Get(window)->IsContainer();
+}
+
+}  // namespace
+
+DisconnectedAppHandler::DisconnectedAppHandler(::mus::Window* root_window) {
+  WmWindowMus* root = WmWindowMus::Get(root_window);
+  for (int shell_window_id = kShellWindowId_Min;
+       shell_window_id < kShellWindowId_Max; ++shell_window_id) {
+    // kShellWindowId_VirtualKeyboardContainer is lazily created.
+    // TODO(sky): http://crbug.com/616909 .
+    // kShellWindowId_PhantomWindow is not a container, but a window.
+    if (shell_window_id == kShellWindowId_VirtualKeyboardContainer ||
+        shell_window_id == kShellWindowId_PhantomWindow)
+      continue;
+
+// kShellWindowId_MouseCursorContainer is chromeos specific.
+#if !defined(OS_CHROMEOS)
+    if (shell_window_id == kShellWindowId_MouseCursorContainer)
+      continue;
+#endif
+
+    WmWindowMus* container = WmWindowMus::AsWmWindowMus(
+        root->GetChildByShellWindowId(shell_window_id));
+    Add(container->mus_window());
+
+    // Add any pre-existing windows in the container to
+    // |disconnected_app_handler_|.
+    for (::mus::Window* child : container->mus_window()->children()) {
+      if (!IsContainer(child))
+        Add(child);
+    }
+  }
+}
 
 DisconnectedAppHandler::~DisconnectedAppHandler() {}
 
 void DisconnectedAppHandler::OnWindowEmbeddedAppDisconnected(
     ::mus::Window* window) {
-  window->Destroy();
+  if (!IsContainer(window))
+    window->Destroy();
+}
+
+void DisconnectedAppHandler::OnTreeChanging(const TreeChangeParams& params) {
+  if (params.old_parent == params.receiver && IsContainer(params.old_parent))
+    Remove(params.target);
+
+  if (params.new_parent == params.receiver && IsContainer(params.new_parent))
+    Add(params.target);
+
+  ::mus::WindowTracker::OnTreeChanging(params);
 }
 
 }  // namespace mus
 }  // namespace ash