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

components/gcm_driver/gcm_client_impl.h

Index: components/gcm_driver/gcm_client_impl.h
diff --git a/components/gcm_driver/gcm_client_impl.h b/components/gcm_driver/gcm_client_impl.h
index 9e102154b86b20e1cbe8c7ac5d81432a36087b1f..bcbf9ed0ddac3c81f1825ad535bb04d5c6a97384 100644
--- a/components/gcm_driver/gcm_client_impl.h
+++ b/components/gcm_driver/gcm_client_impl.h
@@ -19,6 +19,7 @@
 #include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
 #include "components/gcm_driver/gcm_client.h"
+#include "components/gcm_driver/gcm_message_status.h"
 #include "components/gcm_driver/gcm_stats_recorder_impl.h"
 #include "google_apis/gcm/base/mcs_message.h"
 #include "google_apis/gcm/engine/gcm_store.h"
@@ -121,6 +122,9 @@ class GCMClientImpl
   void Send(const std::string& app_id,
             const std::string& receiver_id,
             const OutgoingMessage& message) override;
+  void SendMessageReceipt(const std::string& message_id,
+                          const std::string& app_id,
+                          GCMMessageStatus status) override;
   void RecordDecryptionFailure(const std::string& app_id,
                                GCMEncryptionProvider::DecryptionResult result)
       override;