[GCM] Adding the OnSendAcknowledgement event

components/gcm_driver/gcm_app_handler.h

Index: components/gcm_driver/gcm_app_handler.h
diff --git a/components/gcm_driver/gcm_app_handler.h b/components/gcm_driver/gcm_app_handler.h
index 6e5cd8fc3b1a8f8a9991e6656e5d2d142fb9b0c7..04d1abf7b274c5cf3e4160373cb8813407e0150b 100644
--- a/components/gcm_driver/gcm_app_handler.h
+++ b/components/gcm_driver/gcm_app_handler.h
@@ -36,6 +36,10 @@ class GCMAppHandler {
       const std::string& app_id,
       const GCMClient::SendErrorDetails& send_error_details) = 0;
 
+  // Called when a GCM message was received by GCM server.
+  virtual void OnSendAcknowledged(const std::string& app_id,
+                                  const std::string& message_id) = 0;
+
   // 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.