Fix shelf alignment locking for power button.

ash/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/shelf/shelf_locking_manager.h"
 
 #include "ash/session/session_state_delegate.h"
 #include "ash/shelf/shelf.h"
 #include "ash/shell.h"
 #include "ash/wm/lock_state_controller.h"
@@ skipping 23 matching lines @@
   UpdateLockedState();
 }
 
 void ShelfLockingManager::SessionStateChanged(
     SessionStateDelegate::SessionState state) {
   session_locked_ = state != SessionStateDelegate::SESSION_STATE_ACTIVE;
   UpdateLockedState();
 }
 
 void ShelfLockingManager::OnLockStateEvent(EventType event) {
-  // This is only called when locking the screen; there is no unlock event here.
-  // It's also called when the screen lock animation begins and should help the
-  // shelf appear locked much earlier than ShellObserver::OnLockStateChanged.
-  screen_locked_ = true;
+  // Lock when the animation starts, ignoring pre-lock. There's no unlock event.
+  screen_locked_ |= event == EVENT_LOCK_ANIMATION_STARTED;
   UpdateLockedState();
 }
 
 void ShelfLockingManager::UpdateLockedState() {
   const wm::ShelfAlignment alignment = shelf_->alignment();
   if (is_locked() && alignment != wm::SHELF_ALIGNMENT_BOTTOM_LOCKED) {
     stored_alignment_ = alignment;
     shelf_->SetAlignment(wm::SHELF_ALIGNMENT_BOTTOM_LOCKED);
   } else if (!is_locked() && alignment == wm::SHELF_ALIGNMENT_BOTTOM_LOCKED) {
     shelf_->SetAlignment(stored_alignment_);
   }
 }
 
 }  // namespace ash