Add non-blocking sync code to ProfileSyncService

sync/internal_api/sync_manager_impl.cc

 // Copyright (c) 2012 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 "sync/internal_api/sync_manager_impl.h"
 
 #include <string>
 
 #include "base/base64.h"
 #include "base/bind.h"
@@ skipping 1051 matching lines @@
 
 void SyncManagerImpl::SaveChanges() {
   directory()->SaveChanges();
 }
 
 UserShare* SyncManagerImpl::GetUserShare() {
   DCHECK(initialized_);
   return &share_;
 }
 
-syncer::SyncCore* SyncManagerImpl::GetSyncCore() {
+base::WeakPtr<syncer::SyncCore> SyncManagerImpl::GetSyncCore() {
   DCHECK(initialized_);
-  return sync_core_.get();
+  return sync_core_->AsWeakPtr();
 }
 
 const std::string SyncManagerImpl::cache_guid() {
   DCHECK(initialized_);
   return directory()->cache_guid();
 }
 
 bool SyncManagerImpl::ReceivedExperiment(Experiments* experiments) {
   ReadTransaction trans(FROM_HERE, GetUserShare());
   ReadNode nigori_node(&trans);
@@ skipping 80 matching lines @@
 int SyncManagerImpl::GetDefaultNudgeDelay() {
   return kDefaultNudgeDelayMilliseconds;
 }
 
 // static.
 int SyncManagerImpl::GetPreferencesNudgeDelay() {
   return kPreferencesNudgeDelayMilliseconds;
 }
 
 }  // namespace syncer