[GCM] Observe the event listener adding such that GCM can be started

chrome/browser/extensions/api/gcm/gcm_api.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 CHROME_BROWSER_EXTENSIONS_API_GCM_GCM_API_H_
 #define CHROME_BROWSER_EXTENSIONS_API_GCM_GCM_API_H_
 
 #include "chrome/browser/services/gcm/gcm_event_router.h"
 #include "chrome/common/extensions/api/gcm.h"
+#include "extensions/browser/event_router.h"
 #include "extensions/browser/extension_function.h"
 #include "google_apis/gcm/gcm_client.h"
 
 namespace gcm {
 class GCMProfileService;
 }  // namespace gcm
 
 class Profile;
 
 namespace extensions {
@@ skipping 48 matching lines @@
 
  private:
   void CompleteFunctionWithResult(const std::string& message_id,
                                   gcm::GCMClient::Result result);
 
   // Validates that message data do not carry invalid keys and fit into
   // allowable size limits.
   bool ValidateMessageData(const gcm::GCMClient::MessageData& data) const;
 };
 
-class GcmJsEventRouter : public gcm::GCMEventRouter {
+class GcmJsEventRouter : public gcm::GCMEventRouter,
+                         public EventRouter::Observer {
  public:
   explicit GcmJsEventRouter(Profile* profile);
 
   virtual ~GcmJsEventRouter();
 
   // GCMEventRouter:
   virtual void OnMessage(
       const std::string& app_id,
       const gcm::GCMClient::IncomingMessage& message) OVERRIDE;
   virtual void OnMessagesDeleted(const std::string& app_id) OVERRIDE;
   virtual void OnSendError(const std::string& app_id,
                            const std::string& message_id,
                            gcm::GCMClient::Result result) OVERRIDE;
 
+  // EventRouter::Observer:
+  virtual void OnListenerAdded(const EventListenerInfo& details) OVERRIDE;
+
  private:
   // The application we route the event to is running in context of the
   // |profile_| and the latter outlives the event router.
   Profile* profile_;
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_API_GCM_GCM_API_H_