Fix shelf alignment locking for power button.

ash/shelf/shelf_locking_manager.cc

Index: ash/shelf/shelf_locking_manager.cc
diff --git a/ash/shelf/shelf_locking_manager.cc b/ash/shelf/shelf_locking_manager.cc
index 93c8832b9e09b75b5a7f16d16a8fd5940e8b70f6..d82177ec89e116a552e989e06cd1ac040d97ff03 100644
--- a/ash/shelf/shelf_locking_manager.cc
+++ b/ash/shelf/shelf_locking_manager.cc
@@ -41,10 +41,8 @@ void ShelfLockingManager::SessionStateChanged(
 }
 
 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();
 }