Moves some shutdown related code to earlier on in function

ash/root_window_controller.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/root_window_controller.h"
 
 #include <queue>
 #include <vector>
 
 #include "ash/aura/aura_layout_manager_adapter.h"
@@ skipping 542 matching lines @@
   // panel_layout_manager_ needs to be shut down before windows are destroyed.
   if (panel_layout_manager_) {
     panel_layout_manager_->Shutdown();
     panel_layout_manager_ = NULL;
   }
   // docked_layout_manager_ needs to be shut down before windows are destroyed.
   if (docked_layout_manager_) {
     docked_layout_manager_->Shutdown();
     docked_layout_manager_ = NULL;
   }
-  aura::Window* root_window = GetRootWindow();
-  aura::client::SetDragDropClient(root_window, NULL);
-
   wm_shelf_aura_->ShutdownShelfWidget();
 
   // Close wallpaper widget first as it depends on tooltip.
   wallpaper_widget_controller_.reset();
   animating_wallpaper_widget_controller_.reset();
 
   wm_root_window_controller_->DeleteWorkspaceController();
-  aura::client::SetTooltipClient(root_window, NULL);
 
   // Explicitly destroy top level windows. We do this as during part of
   // destruction such windows may query the RootWindow for state.
+  aura::Window* root_window = GetRootWindow();
   aura::WindowTracker non_toplevel_windows;
   non_toplevel_windows.Add(root_window);
   while (!non_toplevel_windows.windows().empty()) {
     const aura::Window* non_toplevel_window =
         *non_toplevel_windows.windows().begin();
     non_toplevel_windows.Remove(const_cast<aura::Window*>(non_toplevel_window));
     aura::WindowTracker toplevel_windows;
     for (size_t i = 0; i < non_toplevel_window->children().size(); ++i) {
       aura::Window* child = non_toplevel_window->children()[i];
       if (!child->owned_by_parent())
@@ skipping 15 matching lines @@
       root_window->RemoveChild(window);
     }
   }
 
   wm_shelf_aura_->DestroyShelfWidget();
 
   // CloseChildWindows may be called twice during the shutdown of ash unittests.
   // Avoid notifying WmShelf that the shelf has been destroyed twice.
   if (wm_shelf_aura_->IsShelfInitialized())
     wm_shelf_aura_->ShutdownShelf();
+
+  aura::client::SetDragDropClient(root_window, nullptr);
+  aura::client::SetTooltipClient(root_window, nullptr);
 }
 
 void RootWindowController::MoveWindowsTo(aura::Window* dst) {
   // Clear the workspace controller, so it doesn't incorrectly update the shelf.
   wm_root_window_controller_->DeleteWorkspaceController();
   ReparentAllWindows(GetRootWindow(), dst);
 }
 
 ShelfLayoutManager* RootWindowController::GetShelfLayoutManager() {
   return wm_shelf_aura_->shelf_layout_manager();
@@ skipping 328 matching lines @@
     aura::Window* primary_root_window = Shell::GetInstance()
                                             ->window_tree_host_manager()
                                             ->GetPrimaryRootWindow();
     return GetRootWindowSettings(primary_root_window)->controller;
   }
 
   return GetRootWindowSettings(root_window)->controller;
 }
 
 }  // namespace ash