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

components/gcm_driver/fake_gcm_client.cc

Index: components/gcm_driver/fake_gcm_client.cc
diff --git a/components/gcm_driver/fake_gcm_client.cc b/components/gcm_driver/fake_gcm_client.cc
index eaa66c894d182fea831ea919e8b275cdc9edd992..0f36ebaf1cf47688cde72322b9af51e54f4bc739 100644
--- a/components/gcm_driver/fake_gcm_client.cc
+++ b/components/gcm_driver/fake_gcm_client.cc
@@ -18,6 +18,7 @@
 #include "base/threading/thread_task_runner_handle.h"
 #include "base/time/time.h"
 #include "base/timer/timer.h"
+#include "components/sync/base/bind_to_task_runner.h"
 #include "google_apis/gcm/base/encryptor.h"
 #include "google_apis/gcm/engine/account_mapping.h"
 #include "net/base/ip_endpoint.h"
@@ -238,15 +239,26 @@ void FakeGCMClient::PerformDelayedStart() {
 }
 
 void FakeGCMClient::ReceiveMessage(const std::string& app_id,
+                                   const std::string& message_id,
                                    const IncomingMessage& message) {
   DCHECK(ui_thread_->RunsTasksOnCurrentThread());
 
   io_thread_->PostTask(
-      FROM_HERE,
-      base::Bind(&FakeGCMClient::MessageReceived,
-                 weak_ptr_factory_.GetWeakPtr(),
-                 app_id,
-                 message));
+      FROM_HERE, base::Bind(&FakeGCMClient::MessageReceived,
+                            weak_ptr_factory_.GetWeakPtr(), app_id, message,
+                            base::Bind(&FakeGCMClient::SendMessageReceipt,
+                                       weak_ptr_factory_.GetWeakPtr(),
+                                       message_id, app_id)));
+}
+
+void FakeGCMClient::SendMessageReceipt(const std::string& message_id,
+                                       const std::string& app_id,
+                                       GCMMessageStatus status) {
+  DCHECK(io_thread_->RunsTasksOnCurrentThread());
+
+  receipt_message_id_ = message_id;
+  receipt_app_id_ = app_id;
+  receipt_status_ = status;
 }
 
 void FakeGCMClient::DeleteMessages(const std::string& app_id) {
@@ -302,10 +314,13 @@ void FakeGCMClient::SendFinished(const std::string& app_id,
   }
 }
 
-void FakeGCMClient::MessageReceived(const std::string& app_id,
-                                    const IncomingMessage& message) {
+void FakeGCMClient::MessageReceived(
+    const std::string& app_id,
+    const IncomingMessage& message,
+    const GCMClient::MessageReceiptCallback& callback) {
   if (delegate_)
-    delegate_->OnMessageReceived(app_id, message);
+    delegate_->OnMessageReceived(app_id, message,
+                                 syncer::BindToCurrentThread(callback));
 }
 
 void FakeGCMClient::MessagesDeleted(const std::string& app_id) {