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

components/gcm_driver/gcm_account_mapper.h

Index: components/gcm_driver/gcm_account_mapper.h
diff --git a/components/gcm_driver/gcm_account_mapper.h b/components/gcm_driver/gcm_account_mapper.h
index 39cd4dd792e3969450a73cb3d06097be6413f16f..34ff0de2af7568d1cef34e22d2720863d8e658b0 100644
--- a/components/gcm_driver/gcm_account_mapper.h
+++ b/components/gcm_driver/gcm_account_mapper.h
@@ -14,6 +14,7 @@
 #include "base/memory/weak_ptr.h"
 #include "components/gcm_driver/gcm_app_handler.h"
 #include "components/gcm_driver/gcm_client.h"
+#include "components/gcm_driver/gcm_message_status.h"
 #include "google_apis/gcm/engine/account_mapping.h"
 
 namespace base {
@@ -30,9 +31,10 @@ class GCMAccountMapper : public GCMAppHandler {
  public:
   // List of account mappings.
   typedef std::vector<AccountMapping> AccountMappings;
-  typedef base::Callback<void(const std::string& app_id,
-                              const IncomingMessage& message)>
-      DispatchMessageCallback;
+  using DispatchMessageCallback =
+      base::Callback<void(const std::string& app_id,
+                          const IncomingMessage& message,
+                          const MessageReceiptCallback& receipt_callback)>;
 
   explicit GCMAccountMapper(GCMDriver* gcm_driver);
   ~GCMAccountMapper() override;