Fix some minor typos related to the word "accessibility".

ash/system/tray_accessibility.h

 // Copyright (c) 2012 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_TRAY_ACCESSIBILITY_H_
 #define ASH_SYSTEM_TRAY_ACCESSIBILITY_H_
 
 #include "ash/accessibility_delegate.h"
 #include "ash/shell_observer.h"
 #include "ash/system/tray/tray_details_view.h"
@@ skipping 16 matching lines @@
 }
 
 namespace ash {
 class HoverHighlightView;
 class SystemTrayItem;
 
 class ASH_EXPORT AccessibilityObserver {
  public:
   virtual ~AccessibilityObserver() {}
 
-  // Notifies when accessibilty mode changes.
+  // Notifies when accessibility mode changes.
   virtual void OnAccessibilityModeChanged(
       ui::AccessibilityNotificationVisibility notify) = 0;
 };
 
 
 namespace tray {
 
 class AccessibilityPopupView : public TrayNotificationView {
  public:
   AccessibilityPopupView(SystemTrayItem* owner, uint32 enabled_state_bits);
@@ skipping 94 matching lines @@
   // A11y feature status on just entering the lock screen.
   bool show_a11y_menu_on_lock_screen_;
 
   friend class chromeos::TrayAccessibilityTest;
   DISALLOW_COPY_AND_ASSIGN(TrayAccessibility);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_TRAY_ACCESSIBILITY_H_