[Sync] Refactored ProfileSyncService and remove its backend() function

chrome/browser/sync/glue/sync_backend_host.cc

Index: chrome/browser/sync/glue/sync_backend_host.cc
diff --git a/chrome/browser/sync/glue/sync_backend_host.cc b/chrome/browser/sync/glue/sync_backend_host.cc
index 3e600e1c4f4cbb47655bd0c5337df7edad5126ef..06d273a8c55803ff14bf58f395c2fc9bd00ca3cf 100644
--- a/chrome/browser/sync/glue/sync_backend_host.cc
+++ b/chrome/browser/sync/glue/sync_backend_host.cc
@@ -51,12 +51,12 @@ namespace browser_sync {
 using sessions::SyncSessionSnapshot;
 using sync_api::SyncCredentials;
 
-SyncBackendHost::SyncBackendHost(SyncFrontend* frontend, Profile* profile)
+SyncBackendHost::SyncBackendHost(Profile* profile)
     : core_(new Core(ALLOW_THIS_IN_INITIALIZER_LIST(this))),
       core_thread_("Chrome_SyncCoreThread"),
       frontend_loop_(MessageLoop::current()),
       profile_(profile),
-      frontend_(frontend),
+      frontend_(NULL),
       sync_data_folder_path_(
           profile_->GetPath().Append(kSyncDataFolderName)),
       last_auth_error_(AuthError::None()),
@@ -78,6 +78,7 @@ SyncBackendHost::~SyncBackendHost() {
 }
 
 void SyncBackendHost::Initialize(
+    SyncFrontend* frontend,
     const GURL& sync_service_url,
     const syncable::ModelTypeSet& types,
     URLRequestContextGetter* baseline_context_getter,
@@ -87,6 +88,9 @@ void SyncBackendHost::Initialize(
   if (!core_thread_.Start())
     return;
 
+  frontend_ = frontend;
+  DCHECK(frontend);
+
   // Create a worker for the UI thread and route bookmark changes to it.
   // TODO(tim): Pull this into a method to reuse.  For now we don't even
   // need to lock because we init before the syncapi exists and we tear down