Fix accelerator history tracking

ui/base/accelerators/accelerator_history.h

 // Copyright 2014 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 UI_BASE_ACCELERATORS_ACCELERATOR_HISTORY_H_
 #define UI_BASE_ACCELERATORS_ACCELERATOR_HISTORY_H_
 
+#include <set>
+
 #include "base/macros.h"
-#include "base/memory/singleton.h"
 #include "ui/base/accelerators/accelerator.h"
 #include "ui/base/ui_base_export.h"
-#include "ui/events/event.h"
-#include "ui/events/event_handler.h"
 
 namespace ui {
 
 // Keeps track of the system-wide current and the most recent previous
 // key accelerators.
 class UI_BASE_EXPORT AcceleratorHistory {
  public:
   AcceleratorHistory();
   ~AcceleratorHistory();
 
   // Returns the most recent recorded accelerator.
   const Accelerator& current_accelerator() const {
     return current_accelerator_;
   }
 
   // Returns the most recent previously recorded accelerator that is different
   // than the current.
   const Accelerator& previous_accelerator() const {
     return previous_accelerator_;
   }
 
   // Stores the given |accelerator| only if it's different than the currently
   // stored one.
   void StoreCurrentAccelerator(const Accelerator& accelerator);
 
  private:
   Accelerator current_accelerator_;
   Accelerator previous_accelerator_;
 
+  std::set<KeyboardCode> currently_pressed_keys_;
+
   DISALLOW_COPY_AND_ASSIGN(AcceleratorHistory);
 };
 
 }; // namespace ui
 
 #endif  // UI_BASE_ACCELERATORS_ACCELERATOR_HISTORY_H_