[Sync] Try to fix race conditions in CookieJarMismatch.

components/sync/engine/fake_sync_engine.cc

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/sync/engine/fake_sync_engine.h"
 
 #include "components/sync/engine/activation_context.h"
 #include "components/sync/engine/sync_engine_host.h"
 
 namespace syncer {
@@ skipping 79 matching lines @@
 
 void FakeSyncEngine::set_fail_initial_download(bool should_fail) {
   fail_initial_download_ = should_fail;
 }
 
 void FakeSyncEngine::ClearServerData(
     const SyncManager::ClearServerDataCallback& callback) {
   callback.Run();
 }
 
-void FakeSyncEngine::OnCookieJarChanged(bool account_mismatch, bool empty_jar) {
+void FakeSyncEngine::OnCookieJarChanged(bool account_mismatch,
+                                        bool empty_jar,
+                                        const base::Closure& callback) {
+  if (!callback.is_null()) {
+    callback.Run();
+  }
 }
 
 }  // namespace syncer