First pass at experimental omnibox API. There are plenty of rough edges and

chrome/browser/extensions/extension_message_service.h

 // Copyright (c) 2010 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 CHROME_BROWSER_EXTENSIONS_EXTENSION_MESSAGE_SERVICE_H_
 #define CHROME_BROWSER_EXTENSIONS_EXTENSION_MESSAGE_SERVICE_H_
 
 #include <map>
 #include <set>
 #include <string>
@@ skipping 56 matching lines @@
   explicit ExtensionMessageService(Profile* profile);
 
   // Notification that our owning profile is going away.
   void ProfileDestroyed();
 
   // Add or remove |render_process_pid| as a listener for |event_name|.
   void AddEventListener(const std::string& event_name, int render_process_id);
   void RemoveEventListener(const std::string& event_name,
                            int render_process_id);
 
+  // Returns true if there is at least one listener for the given event.
+  bool HasEventListener(const std::string& event_name);
+
   // Closes the message channel associated with the given port, and notifies
   // the other side.
   void CloseChannel(int port_id);
 
   // Sends a message from a renderer to the given port.
   void PostMessageFromRenderer(int port_id, const std::string& message);
 
   // Send an event to every registered extension renderer.  If
   // |has_incognito_data| is true, the event is only sent to extension with the
   // permission to access incognito data. If |event_url| is not empty, the
@@ skipping 114 matching lines @@
   int next_port_id_;
 
   // Protects the next_port_id_ variable, since it can be
   // used on the IO thread or the UI thread.
   Lock next_port_id_lock_;
 
   DISALLOW_COPY_AND_ASSIGN(ExtensionMessageService);
 };
 
 #endif  // CHROME_BROWSER_EXTENSIONS_EXTENSION_MESSAGE_SERVICE_H_