[Sync] Try to fix race conditions in CookieJarMismatch.

components/sync/driver/glue/sync_backend_host_core.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/driver/glue/sync_backend_host_core.h"
 
 #include <utility>
 
 #include "base/bind.h"
 #include "base/files/file_util.h"
@@ skipping 567 matching lines @@
 void SyncBackendHostCore::DoClearServerData(
     const SyncManager::ClearServerDataCallback& frontend_callback) {
   DCHECK(thread_checker_.CalledOnValidThread());
   const SyncManager::ClearServerDataCallback callback =
       base::Bind(&SyncBackendHostCore::ClearServerDataDone,
                  weak_ptr_factory_.GetWeakPtr(), frontend_callback);
   sync_manager_->ClearServerData(callback);
 }
 
 void SyncBackendHostCore::DoOnCookieJarChanged(bool account_mismatch,
-                                               bool empty_jar) {
+                                               bool empty_jar,
+                                               const base::Closure& callback) {
   DCHECK(thread_checker_.CalledOnValidThread());
   sync_manager_->OnCookieJarChanged(account_mismatch, empty_jar);
+  if (!callback.is_null()) {
+    host_.Call(FROM_HERE,
+               &SyncBackendHostImpl::OnCookieJarChangedDoneOnFrontendLoop,
+               callback);
+  }
 }
 
 void SyncBackendHostCore::ClearServerDataDone(
     const base::Closure& frontend_callback) {
   DCHECK(thread_checker_.CalledOnValidThread());
   host_.Call(FROM_HERE, &SyncBackendHostImpl::ClearServerDataDoneOnFrontendLoop,
              frontend_callback);
 }
 
 }  // namespace syncer