Revert "chromeos: Move files in //ash/common to //ash, part 1"

ash/system/accessibility_observer.h

Index: ash/system/accessibility_observer.h
diff --git a/ash/system/accessibility_observer.h b/ash/system/accessibility_observer.h
deleted file mode 100644
index fb6b937176c71c5f64c2a041b915ffa7468e8c32..0000000000000000000000000000000000000000
--- a/ash/system/accessibility_observer.h
+++ /dev/null
@@ -1,24 +0,0 @@
-// 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_SYSTEM_ACCESSIBILITY_OBSERVER_H_
-#define ASH_SYSTEM_ACCESSIBILITY_OBSERVER_H_
-
-#include "ash/ash_export.h"
-#include "ash/common/accessibility_types.h"
-
-namespace ash {
-
-class ASH_EXPORT AccessibilityObserver {
- public:
-  virtual ~AccessibilityObserver() {}
-
-  // Notifies when accessibility mode changes.
-  virtual void OnAccessibilityModeChanged(
-      AccessibilityNotificationVisibility notify) = 0;
-};
-
-}  // namespace ash
-
-#endif  // ASH_SYSTEM_ACCESSIBILITY_OBSERVER_H_