chromeos: Refactor shelf to create ShelfView earlier in startup

ash/shelf/shelf_locking_manager.h

 // 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.
 
 #ifndef ASH_SHELF_SHELF_LOCKING_MANAGER_H_
 #define ASH_SHELF_SHELF_LOCKING_MANAGER_H_
 
 #include "ash/ash_export.h"
 #include "ash/public/cpp/shelf_types.h"
 #include "ash/session/session_observer.h"
 #include "ash/wm/lock_state_observer.h"
 
 namespace ash {
 
 class WmShelf;
 
-// ShelfLockingManager observes screen and session events to [un]lock the shelf.
+// ShelfLockingManager observes screen and session events to align the shelf at
+// the bottom of the screen when the screen is locked.
 class ASH_EXPORT ShelfLockingManager : public SessionObserver,
                                        public LockStateObserver {
  public:
   explicit ShelfLockingManager(WmShelf* shelf);
   ~ShelfLockingManager() override;
 
   bool is_locked() const { return session_locked_ || screen_locked_; }
   void set_stored_alignment(ShelfAlignment value) { stored_alignment_ = value; }
 
   // SessionObserver:
@@ skipping 13 matching lines @@
   ShelfAlignment stored_alignment_;
 
   ScopedSessionObserver scoped_session_observer_;
 
   DISALLOW_COPY_AND_ASSIGN(ShelfLockingManager);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SHELF_SHELF_LOCKING_MANAGER_H_