mash: Avoid shelf crashes on display removal.

ash/common/shelf/shelf_layout_manager.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/common/shelf/shelf_layout_manager.h"
 
 #include <algorithm>
 #include <cmath>
 #include <vector>
 
@@ skipping 180 matching lines @@
       return SHELF_AUTO_HIDE;
     case SHELF_AUTO_HIDE_BEHAVIOR_NEVER:
       return SHELF_VISIBLE;
     case SHELF_AUTO_HIDE_ALWAYS_HIDDEN:
       return SHELF_HIDDEN;
   }
   return SHELF_VISIBLE;
 }
 
 void ShelfLayoutManager::UpdateVisibilityState() {
+  // Bail out early before the shelf is initialized or after it is destroyed.
   WmWindow* shelf_window = WmLookup::Get()->GetWindowForWidget(shelf_widget_);
-  WmRootWindowController* controller = shelf_window->GetRootWindowController();
-  // Bail out early before the shelf is initialized or after it is destroyed.
-  if (!controller || !wm_shelf_->IsShelfInitialized() || in_shutdown_)
+  if (in_shutdown_ || !wm_shelf_->IsShelfInitialized() || !shelf_window)
     return;
   bool was_invisible_auto_hide_shelf = invisible_auto_hide_shelf_;
   // Always reset to be safe.
   invisible_auto_hide_shelf_ = false;
   if (state_.is_screen_locked || state_.is_adding_user_screen) {
     SetState(SHELF_VISIBLE);
   } else if (WmShell::Get()->IsPinned()) {
     SetState(SHELF_HIDDEN);
   } else {
     // TODO(zelidrag): Verify shelf drag animation still shows on the device
     // when we are in SHELF_AUTO_HIDE_ALWAYS_HIDDEN.
     wm::WorkspaceWindowState window_state(
-        controller->GetWorkspaceWindowState());
+        shelf_window->GetRootWindowController()->GetWorkspaceWindowState());
     switch (window_state) {
       case wm::WORKSPACE_WINDOW_STATE_FULL_SCREEN: {
         switch (GetShelfModeForFullscreen()) {
           case wm::WindowState::SHELF_HIDDEN:
             SetState(SHELF_HIDDEN);
             break;
           case wm::WindowState::SHELF_AUTO_HIDE_INVISIBLE:
             invisible_auto_hide_shelf_ = true;
           case wm::WindowState::SHELF_AUTO_HIDE_VISIBLE:
             if (was_invisible_auto_hide_shelf != invisible_auto_hide_shelf_ &&
@@ skipping 911 matching lines @@
   gesture_drag_status_ = GESTURE_DRAG_NONE;
 }
 
 int ShelfLayoutManager::GetShelfInsetsForAutoHide() const {
   if (invisible_auto_hide_shelf_)
     return 0;
   return GetShelfConstant(SHELF_INSETS_FOR_AUTO_HIDE);
 }
 
 }  // namespace ash