Convert TrayAccessibility to wm common types

ash/common/system/accessibility_observer.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_COMMON_SYSTEM_ACCESSIBILITY_OBSERVER_H_
+#define ASH_COMMON_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(
+      ui::AccessibilityNotificationVisibility notify) = 0;
+};
+
+}  // namespace ash
+
+#endif  // ASH_COMMON_SYSTEM_ACCESSIBILITY_OBSERVER_H_