Push API: register PushMessagingServiceImpl as GCMAppHandler.

components/gcm_driver/gcm_app_handler.h

 // Copyright (c) 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 COMPONENTS_GCM_DRIVER_GCM_APP_HANDLER_H_
 #define COMPONENTS_GCM_DRIVER_GCM_APP_HANDLER_H_
 
 #include <string>
 
 #include "base/basictypes.h"
@@ skipping 27 matching lines @@
 
   // Called when a new connection is established and a successful handshake
   // has been performed. Note that |ip_endpoint| is only set if available for
   // the current platform.
   // Default implementation does nothing.
   virtual void OnConnected(const net::IPEndPoint& ip_endpoint);
 
   // Called when the connection is interrupted.
   // Default implementation does nothing.
   virtual void OnDisconnected();
+
+  // If no app handler has been added with the exact app_id of an incoming
+  // event, all handlers will be asked (in arbitrary order) whether they can
+  // handle the app_id, and the first to return true will receive the event.
+  virtual bool CanHandle(const std::string& app_id);
 };
 
 }  // namespace gcm
 
 #endif  // COMPONENTS_GCM_DRIVER_GCM_APP_HANDLER_H_