events: Introduce EventRewriter.

ui/events/event_source.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 UI_EVENTS_EVENT_SOURCE_H_
 #define UI_EVENTS_EVENT_SOURCE_H_
 
+#include <vector>
+
 #include "ui/events/event_dispatcher.h"
 #include "ui/events/events_export.h"
 
 namespace ui {
 
 class Event;
 class EventProcessor;
+class EventRewriter;
 
 // EventSource receives events from the native platform (e.g. X11, win32 etc.)
 // and sends the events to an EventProcessor.
 class EVENTS_EXPORT EventSource {
  public:
-  virtual ~EventSource() {}
+  EventSource();
+  virtual ~EventSource();
 
   virtual EventProcessor* GetEventProcessor() = 0;
 
+  // Adds a rewriter to modify events before they are sent to the
+  // EventProcessor. The rewriter must be explicitly removed from the
+  // EventSource before the rewriter is destroyed. The EventSource
+  // does not take ownership of the rewriter.
+  void AddEventRewriter(EventRewriter* rewriter);
+  void RemoveEventRewriter(EventRewriter* rewriter);
+
  protected:
   EventDispatchDetails SendEventToProcessor(Event* event);
+
+ private:
+  typedef std::vector<EventRewriter*> EventRewriterList;
+  EventDispatchDetails DeliverEventToProcessor(Event* event);
+  EventRewriterList rewriter_list_;
+  DISALLOW_COPY_AND_ASSIGN(EventSource);
 };
 
 }  // namespace ui
 
 #endif // UI_EVENTS_EVENT_SOURCE_H_