Make it clear what last_sync_timestamp actually tracks. Update

chrome/browser/sync/engine/syncer_end_command.cc

 // Copyright (c) 2009 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 "chrome/browser/sync/engine/syncer_end_command.h"
 
 #include "chrome/browser/sync/engine/syncer_types.h"
 #include "chrome/browser/sync/sessions/sync_session.h"
 #include "chrome/browser/sync/syncable/directory_manager.h"
 #include "chrome/browser/sync/util/event_sys-inl.h"
 
 namespace browser_sync {
 
 SyncerEndCommand::SyncerEndCommand() {}
 SyncerEndCommand::~SyncerEndCommand() {}
 
 void SyncerEndCommand::ExecuteImpl(sessions::SyncSession* session) {
   sessions::StatusController* status(session->status_controller());
   status->set_syncing(false);
 
-  if (!session->HasMoreToSync()) {
-    // This might be the first time we've fully completed a sync cycle.
-    DCHECK(status->got_zero_updates());
-
+  // This might be the first time we've fully completed a sync cycle.
+  if (!session->HasMoreToSync() &&
+      status->server_says_nothing_more_to_download()) {
     syncable::ScopedDirLookup dir(session->context()->directory_manager(),
                                   session->context()->account_name());
     if (!dir.good()) {
       LOG(ERROR) << "Scoped dir lookup failed!";
       return;
     }
 
     // This gets persisted to the directory's backing store.
     dir->set_initial_sync_ended(true);
   }
 
   SyncerEvent event(SyncerEvent::SYNC_CYCLE_ENDED);
   sessions::SyncSessionSnapshot snapshot(session->TakeSnapshot());
   event.snapshot = &snapshot;
   session->context()->syncer_event_channel()->NotifyListeners(event);
 }
 
 }  // namespace browser_sync