Moves maintaining ShellObservers back to Shell

ash/common/system/overview/overview_button_tray.cc

 // Copyright 2014 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/system/overview/overview_button_tray.h"
 
 #include "ash/common/session/session_state_delegate.h"
 #include "ash/common/shelf/shelf_constants.h"
 #include "ash/common/system/tray/system_tray_delegate.h"
 #include "ash/common/system/tray/tray_constants.h"
 #include "ash/common/wm/maximize_mode/maximize_mode_controller.h"
 #include "ash/common/wm/overview/window_selector_controller.h"
 #include "ash/common/wm_shell.h"
 #include "ash/resources/vector_icons/vector_icons.h"
+#include "ash/shell.h"
 #include "ash/strings/grit/ash_strings.h"
 #include "ui/base/l10n/l10n_util.h"
 #include "ui/gfx/paint_vector_icon.h"
 #include "ui/views/border.h"
 #include "ui/views/controls/image_view.h"
 
 namespace ash {
 
 OverviewButtonTray::OverviewButtonTray(WmShelf* wm_shelf)
     : TrayBackgroundView(wm_shelf), icon_(new views::ImageView()) {
   SetInkDropMode(InkDropMode::ON);
   SetContentsBackground(false);
 
   icon_->SetImage(CreateVectorIcon(kShelfOverviewIcon, kShelfIconColor));
   SetIconBorderForShelfAlignment();
   tray_container()->AddChildView(icon_);
 
   // Since OverviewButtonTray is located on the rightmost position of a
   // horizontal shelf, no separator is required.
   set_separator_visibility(false);
 
-  WmShell::Get()->AddShellObserver(this);
+  Shell::GetInstance()->AddShellObserver(this);
   WmShell::Get()->GetSessionStateDelegate()->AddSessionStateObserver(this);
 }
 
 OverviewButtonTray::~OverviewButtonTray() {
-  WmShell::Get()->RemoveShellObserver(this);
+  Shell::GetInstance()->RemoveShellObserver(this);
   WmShell::Get()->GetSessionStateDelegate()->RemoveSessionStateObserver(this);
 }
 
 void OverviewButtonTray::UpdateAfterLoginStatusChange(LoginStatus status) {
   UpdateIconVisibility();
 }
 
 bool OverviewButtonTray::PerformAction(const ui::Event& event) {
   WindowSelectorController* controller =
       WmShell::Get()->window_selector_controller();
@@ skipping 67 matching lines @@
       !session_state_delegate->IsScreenLocked() &&
       session_state_delegate->GetSessionState() ==
           session_manager::SessionState::ACTIVE &&
       shell->system_tray_delegate()->GetUserLoginStatus() !=
           LoginStatus::KIOSK_APP &&
       shell->system_tray_delegate()->GetUserLoginStatus() !=
           LoginStatus::ARC_KIOSK_APP);
 }
 
 }  // namespace ash