Sticky keys modifies an entire scroll sequence instead of just a single event.

ash/wm/sticky_keys.h

 // Copyright 2013 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_WM_STICKY_KEYS_H_
 #define ASH_WM_STICKY_KEYS_H_
 
 #include "ash/ash_export.h"
 #include "base/memory/scoped_ptr.h"
 #include "ui/events/event_constants.h"
@@ skipping 204 matching lines @@
 
   // True if the received key event is sent by StickyKeyHandler.
   bool event_from_myself_;
 
   // True if we received the TARGET_MODIFIER_DOWN event while in the DISABLED
   // state but before we receive the TARGET_MODIFIER_UP event. Normal
   // shortcuts (eg. ctrl + t) during this time will prevent a transition to
   // the ENABLED state.
   bool preparing_to_enable_;
 
+  // Tracks the scroll direction of the current scroll sequence. Sticky keys
+  // stops modifying the scroll events of the sequence when the direction
+  // changes. If no sequence is tracked, the value is 0.
+  int scroll_delta_;
+
   // The modifier up key event to be sent on non modifier key on ENABLED state.
   scoped_ptr<ui::KeyEvent> modifier_up_event_;
 
   scoped_ptr<StickyKeysHandlerDelegate> delegate_;
 
   DISALLOW_COPY_AND_ASSIGN(StickyKeysHandler);
 };
 
 }  // namespace ash
 
 #endif  // ASH_WM_STICKY_KEYS_H_