Nix GetRootWindowController, use RootWindowController::ForWindow.

ash/shelf/shelf.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/shelf/shelf.h"
 
 #include "ash/public/cpp/config.h"
 #include "ash/public/cpp/shelf_item_delegate.h"
 #include "ash/public/cpp/shell_window_ids.h"
 #include "ash/root_window_controller.h"
@@ skipping 55 matching lines @@
   // TODO: ShelfBezelEventHandler needs to work with mus too.
   // http://crbug.com/636647
   if (Shell::GetAshConfig() != Config::MASH)
     bezel_event_handler_ = base::MakeUnique<ShelfBezelEventHandler>(this);
 }
 
 Shelf::~Shelf() {}
 
 // static
 Shelf* Shelf::ForWindow(aura::Window* window) {
-  return GetRootWindowController(window->GetRootWindow())->shelf();
+  return RootWindowController::ForWindow(window)->shelf();
 }
 
 // static
 bool Shelf::CanChangeShelfAlignment() {
   if (Shell::Get()->session_controller()->IsUserSupervised())
     return false;
 
   const LoginStatus login_status =
       Shell::Get()->session_controller()->login_status();
 
@@ skipping 270 matching lines @@
 
 void Shelf::OnBackgroundUpdated(ShelfBackgroundType background_type,
                                 AnimationChangeType change_type) {
   if (background_type == GetBackgroundType())
     return;
   for (auto& observer : observers_)
     observer.OnBackgroundTypeChanged(background_type, change_type);
 }
 
 }  // namespace ash