Convert chromeos::EventRewriter to a ui::EventRewriter

ui/events/event_rewriter.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_EVENTS_EVENT_REWRITER_H_
 #define UI_EVENTS_EVENT_REWRITER_H_
 
 #include "base/memory/scoped_ptr.h"
 #include "ui/events/events_export.h"
 
 namespace ui {
 
 class Event;
 
 // Return status of EventRewriter operations; see that class below.
 enum EventRewriteStatus {
   // Nothing was done; no rewritten event returned. Pass the original
   // event to later rewriters, or send it to the EventProcessor if this
   // was the final rewriter.
   EVENT_REWRITE_CONTINUE,
 
-  // The event has been rewritten. Send the rewritten event to the
-  // EventProcessor instead of the original event (without sending
-  // either to any later rewriters).
+  // The event has been rewritten. Send the rewritten event (which may
+  // be either the modified original event, or a newly allocated event)
+  // to the EventProcessor, without sending it to any later rewriters.
   EVENT_REWRITE_REWRITTEN,
 
   // The event should be discarded, neither passing it to any later
   // rewriters nor sending it to the EventProcessor.
   EVENT_REWRITE_DISCARD,
 
   // The event has been rewritten. As for EVENT_REWRITE_REWRITTEN,
-  // send the rewritten event to the EventProcessor instead of the
-  // original event (without sending either to any later rewriters).
-  // In addition the rewriter has one or more additional new events
-  // to be retrieved using |NextDispatchEvent()| and sent to the
-  // EventProcessor.
+  // send the rewritten event to the EventProcessor without invoking
+  // any later rewriters. In addition the rewriter has one or more
+  // additional new events to be retrieved using |NextDispatchEvent()|
+  // and sent to the EventProcessor.
   EVENT_REWRITE_DISPATCH_ANOTHER,
 };
 
 // EventRewriter provides a mechanism for Events to be rewritten
 // before being dispatched from EventSource to EventProcessor.
 class EVENTS_EXPORT EventRewriter {
  public:
   virtual ~EventRewriter() {}
 
-  // Potentially rewrites (replaces) an event, or requests it be discarded.
-  // or discards an event. If the rewriter wants to rewrite an event, and
-  // dispatch another event once the rewritten event is dispatched, it should
-  // return EVENT_REWRITE_DISPATCH_ANOTHER, and return the next event to
+  // Potentially rewrites or replaces an event, or requests it be discarded.
+  // A rewritten event may either be the modified original |event|, or a
+  // newly allocated event returned through |rewritten_event| (but not both).
+  // If the rewriter wants to rewrite an event, and dispatch another
+  // event once the rewritten event is dispatched, it should return
+  // EVENT_REWRITE_DISPATCH_ANOTHER, and return the next event to
   // dispatch from |NextDispatchEvent()|.
   virtual EventRewriteStatus RewriteEvent(
-      const Event& event,
+      Event* event,
       scoped_ptr<Event>* rewritten_event) = 0;
 
   // Supplies an additional event to be dispatched. It is only valid to
   // call this after the immediately previous call to |RewriteEvent()|
   // or |NextDispatchEvent()| has returned EVENT_REWRITE_DISPATCH_ANOTHER.
   // Should only return either EVENT_REWRITE_REWRITTEN or
   // EVENT_REWRITE_DISPATCH_ANOTHER; otherwise the previous call should not
-  // have returned EVENT_REWRITE_DISPATCH_ANOTHER.
+  // have returned EVENT_REWRITE_DISPATCH_ANOTHER. |last_event| must be
+  // the previous rewritten event, and the additional event is returned
+  // through |new_event|.
   virtual EventRewriteStatus NextDispatchEvent(
       const Event& last_event,
       scoped_ptr<Event>* new_event) = 0;
 };
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_EVENT_REWRITER_H_