extensions: Cleanup class/struct fwd declarations

extensions/browser/event_listener_map.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 EXTENSIONS_BROWSER_EVENT_LISTENER_MAP_H_
 #define EXTENSIONS_BROWSER_EVENT_LISTENER_MAP_H_
 
 #include <map>
 #include <memory>
 #include <set>
 #include <string>
 #include <vector>
 
 #include "base/macros.h"
 #include "extensions/common/event_filter.h"
 #include "url/gurl.h"
 
 namespace base {
 class DictionaryValue;
 }
 
 namespace content {
 class BrowserContext;
 class RenderProcessHost;
 }
 
-class ListenerRemovalListener;
-
 namespace extensions {
 struct Event;
 
 // A listener for an extension event. A listener is essentially an endpoint
 // that an event can be dispatched to.
 //
 // This is a lazy listener if |IsLazy| is returns true, and a filtered listener
 // if |filter| is defined.
 //
 // A lazy listener is added to an event to indicate that a lazy background page
@@ skipping 151 matching lines @@
   std::map<EventFilter::MatcherID, EventListener*> listeners_by_matcher_id_;
 
   EventFilter event_filter_;
 
   DISALLOW_COPY_AND_ASSIGN(EventListenerMap);
 };
 
 }  // namespace extensions
 
 #endif  // EXTENSIONS_BROWSER_EVENT_LISTENER_MAP_H_