(Merge to M-51) Revise the shelf alignment locking mechanism.

ash/shelf/shelf_locking_manager.h

Index: ash/shelf/shelf_locking_manager.h
diff --git a/ash/shelf/shelf_locking_manager.h b/ash/shelf/shelf_locking_manager.h
new file mode 100644
index 0000000000000000000000000000000000000000..73878e203c989c9af0f303a4616dc03db006656c
--- /dev/null
+++ b/ash/shelf/shelf_locking_manager.h
@@ -0,0 +1,49 @@
+// 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/session/session_state_observer.h"
+#include "ash/shelf/shelf_types.h"
+#include "ash/shell_observer.h"
+#include "ash/wm/lock_state_observer.h"
+
+namespace ash {
+
+class Shelf;
+
+// ShelfLockingManager observes screen and session events to [un]lock the shelf.
+class ASH_EXPORT ShelfLockingManager : public ShellObserver,
+                                       public SessionStateObserver,
+                                       public LockStateObserver {
+ public:
+  explicit ShelfLockingManager(Shelf* shelf);
+  ~ShelfLockingManager() override;
+
+  // ShellObserver:
+  void OnLockStateChanged(bool locked) override;
+
+  // SessionStateObserver:
+  void SessionStateChanged(SessionStateDelegate::SessionState state) override;
+
+  // LockStateObserver:
+  void OnLockStateEvent(EventType event) override;
+
+ private:
+  // Update the shelf state for session and screen lock changes.
+  void UpdateLockedState();
+
+  Shelf* shelf_;
+  bool session_locked_ = false;
+  bool screen_locked_ = false;
+  ShelfAlignment stored_alignment_ = SHELF_ALIGNMENT_BOTTOM;
+
+  DISALLOW_COPY_AND_ASSIGN(ShelfLockingManager);
+};
+
+}  // namespace ash
+
+#endif  // ASH_SHELF_SHELF_LOCKING_MANAGER_H_