mash: remove more shell/shelf WmWindow usage.

chrome/browser/chromeos/accessibility/chromevox_panel.cc

 // Copyright 2015 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 "chrome/browser/chromeos/accessibility/chromevox_panel.h"
 
 #include "ash/accessibility_types.h"
 #include "ash/public/cpp/shell_window_ids.h"
 #include "ash/root_window_controller.h"
 #include "ash/shelf/shelf_layout_manager.h"
@@ skipping 183 matching lines @@
   if (ash::GetRootWindowController(GetRootWindow())
           ->GetWindowForFullscreenMode() &&
       !widget_->IsActive()) {
     bounds.set_height(0);
   }
 
   widget_->SetBounds(bounds);
 }
 
 void ChromeVoxPanel::SendPanelHeightToAsh(int panel_height) {
-  // WmShelf is available for the lifetime of the RootWindowController.
-  ash::RootWindowController* root_window_controller =
-      ash::RootWindowController::ForWindow(GetRootWindow());
-  if (!root_window_controller)
-    return;
-
   // TODO(mash): Replace with shelf mojo API.
+  ash::WmShelf* shelf = ash::WmShelf::ForWindow(GetRootWindow());
   ash::ShelfLayoutManager* shelf_layout_manager =
-      root_window_controller->GetShelf()->shelf_layout_manager();
+      shelf ? shelf->shelf_layout_manager() : nullptr;
   if (shelf_layout_manager)
     shelf_layout_manager->SetChromeVoxPanelHeight(panel_height);
 }