Re-factor system tray code controlling launcher visibility

ash/wm/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/wm/shelf_layout_manager.h"
 
 #include <algorithm>
 
 #include "ash/launcher/launcher.h"
 #include "ash/screen_ash.h"
@@ skipping 526 matching lines @@
 
 ShelfLayoutManager::AutoHideState ShelfLayoutManager::CalculateAutoHideState(
     VisibilityState visibility_state) const {
   if (visibility_state != AUTO_HIDE || !launcher_widget())
     return AUTO_HIDE_HIDDEN;
 
   Shell* shell = Shell::GetInstance();
   if (shell->GetAppListTargetVisibility())
     return AUTO_HIDE_SHOWN;
 
-  if (shell->system_tray() && shell->system_tray()->should_show_launcher())
+  if (shell->status_area_widget() &&
+      shell->status_area_widget()->should_show_launcher())
     return AUTO_HIDE_SHOWN;
 
   if (launcher_ && launcher_->IsShowingMenu())
     return AUTO_HIDE_SHOWN;
 
   if (launcher_ && launcher_->IsShowingOverflowBubble())
     return AUTO_HIDE_SHOWN;
 
   if (launcher_widget()->IsActive() || status_->IsActive())
     return AUTO_HIDE_SHOWN;
@@ skipping 45 matching lines @@
 int ShelfLayoutManager::GetWorkAreaSize(const State& state, int size) const {
   if (state.visibility_state == VISIBLE)
     return size;
   if (state.visibility_state == AUTO_HIDE)
     return kAutoHideSize;
   return 0;
 }
 
 }  // namespace internal
 }  // namespace ash