Fix sticky keys crash when handling synthetic events without a native event.

ash/sticky_keys/sticky_keys_controller.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_STICKY_KEYS_STICKY_KEYS_CONTROLLER_H_
 #define ASH_STICKY_KEYS_STICKY_KEYS_CONTROLLER_H_
 
 #include "ash/ash_export.h"
 #include "ash/sticky_keys/sticky_keys_state.h"
 #include "base/memory/scoped_ptr.h"
@@ skipping 129 matching lines @@
 //
 // Here, (*) means key event will be consumed by StickyKeys, and (#) means event
 // is modified.
 class ASH_EXPORT StickyKeysHandler {
  public:
   class StickyKeysHandlerDelegate {
    public:
     StickyKeysHandlerDelegate();
     virtual ~StickyKeysHandlerDelegate();
 
-    // Dispatches keyboard event synchronously.
+    // Dispatches keyboard event synchronously. |event| is an event that has
+    // been previously dispatched.
     virtual void DispatchKeyEvent(ui::KeyEvent* event,
                                   aura::Window* target) = 0;
 
-    // Dispatches mouse event synchronously.
+    // Dispatches mouse event synchronously. |event| is an event that has
+    // been previously dispatched.
     virtual void DispatchMouseEvent(ui::MouseEvent* event,
                                     aura::Window* target) = 0;
 
-    // Dispatches scroll event synchronously.
+    // Dispatches scroll event synchronously. |event| is an event that has
+    // been previously dispatched.
     virtual void DispatchScrollEvent(ui::ScrollEvent* event,
                                      aura::Window* target) = 0;
   };
 
   // This class takes an ownership of |delegate|.
   StickyKeysHandler(ui::EventFlags modifier_flag,
                     StickyKeysHandlerDelegate* delegate);
   ~StickyKeysHandler();
 
   // Handles key event. Returns true if key is consumed.
@@ skipping 69 matching lines @@
   scoped_ptr<ui::KeyEvent> modifier_up_event_;
 
   scoped_ptr<StickyKeysHandlerDelegate> delegate_;
 
   DISALLOW_COPY_AND_ASSIGN(StickyKeysHandler);
 };
 
 }  // namespace ash
 
 #endif  // ASH_STICKY_KEYS_STICKY_KEYS_CONTROLLER_H_