Moves maintaining ShellObservers back to Shell

ash/common/shelf/shelf_locking_manager.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/common/shelf/shelf_locking_manager.h"
 
 #include "ash/common/session/session_state_delegate.h"
 #include "ash/common/shelf/wm_shelf.h"
 #include "ash/common/wm_shell.h"
+#include "ash/shell.h"
 
 namespace ash {
 
 ShelfLockingManager::ShelfLockingManager(WmShelf* shelf) : shelf_(shelf) {
   WmShell::Get()->AddLockStateObserver(this);
   SessionStateDelegate* delegate = WmShell::Get()->GetSessionStateDelegate();
   session_locked_ =
       delegate->GetSessionState() != session_manager::SessionState::ACTIVE;
   screen_locked_ = delegate->IsScreenLocked();
   delegate->AddSessionStateObserver(this);
-  WmShell::Get()->AddShellObserver(this);
+  Shell::GetInstance()->AddShellObserver(this);
 }
 
 ShelfLockingManager::~ShelfLockingManager() {
   WmShell::Get()->RemoveLockStateObserver(this);
   WmShell::Get()->GetSessionStateDelegate()->RemoveSessionStateObserver(this);
-  WmShell::Get()->RemoveShellObserver(this);
+  Shell::GetInstance()->RemoveShellObserver(this);
 }
 
 void ShelfLockingManager::OnLockStateChanged(bool locked) {
   screen_locked_ = locked;
   UpdateLockedState();
 }
 
 void ShelfLockingManager::SessionStateChanged(
     session_manager::SessionState state) {
   session_locked_ = state != session_manager::SessionState::ACTIVE;
@@ skipping 10 matching lines @@
   const ShelfAlignment alignment = shelf_->GetAlignment();
   if (is_locked() && alignment != SHELF_ALIGNMENT_BOTTOM_LOCKED) {
     stored_alignment_ = alignment;
     shelf_->SetAlignment(SHELF_ALIGNMENT_BOTTOM_LOCKED);
   } else if (!is_locked() && alignment == SHELF_ALIGNMENT_BOTTOM_LOCKED) {
     shelf_->SetAlignment(stored_alignment_);
   }
 }
 
 }  // namespace ash