Provide a mechanism for the GCM driver to send message receipts to GCM.

components/gcm_driver/gcm_driver.h

Index: components/gcm_driver/gcm_driver.h
diff --git a/components/gcm_driver/gcm_driver.h b/components/gcm_driver/gcm_driver.h
index f115d16562a00f5259063fee96ca738bf8819c74..2cb277128a73bdd80c83be6d74eb66508ba8c3e4 100644
--- a/components/gcm_driver/gcm_driver.h
+++ b/components/gcm_driver/gcm_driver.h
@@ -141,6 +141,13 @@ class GCMDriver {
   void GetEncryptionInfo(const std::string& app_id,
                          const GetEncryptionInfoCallback& callback);
 
+  // Send a message to GCM with information about the final status of a
+  // previously received message. This can berun as a result of a callback being
+  // executed from an AppHandler.
+  void SendMessageReceipt(const std::string& message_id,
+                          const std::string& app_id,
+                          int status);
+
   const GCMAppHandlerMap& app_handlers() const { return app_handlers_; }
 
   // This method must be called before destroying the GCMDriver. Once it has
@@ -199,7 +206,7 @@ class GCMDriver {
   // Updates the |account_mapping| information in persistent store.
   virtual void UpdateAccountMapping(const AccountMapping& account_mapping) = 0;
 
-  // Removes the account mapping information reated to |account_id| from
+  // Removes the account mapping information related to |account_id| from
   // persistent store.
   virtual void RemoveAccountMapping(const std::string& account_id) = 0;
 
@@ -315,6 +322,9 @@ class GCMDriver {
       const UnregisterCallback& unregister_callback,
       GCMClient::Result result);
 
+  void SendMessageReceiptCallback(const std::string& message_id,
+                                  GCMClient::Result result);
+
   // Callback map (from app_id to callback) for Register.
   std::map<std::string, RegisterCallback> register_callbacks_;