Avoid useless SYNC_CYCLE_CONTINUATION sync cycle

chrome/browser/sync/engine/model_changing_syncer_command.cc

 // Copyright (c) 2011 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/model_changing_syncer_command.h"
 
 #include "base/basictypes.h"
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "chrome/browser/sync/sessions/status_controller.h"
 #include "chrome/browser/sync/sessions/sync_session.h"
-#include "chrome/browser/sync/util/unrecoverable_error_info.h"
 
 namespace browser_sync {
 
-void ModelChangingSyncerCommand::ExecuteImpl(sessions::SyncSession* session) {
+SyncerError ModelChangingSyncerCommand::ExecuteImpl(
+    sessions::SyncSession* session) {
   work_session_ = session;
-  if (!ModelNeutralExecuteImpl(work_session_)) {
-    return;
+  SyncerError result = ModelNeutralExecuteImpl(work_session_);
+
+  if (result != NO_ERROR) {
+    return result;
   }
 
   const std::set<ModelSafeGroup>& groups_to_change =
       GetGroupsToChange(*work_session_);
   for (size_t i = 0; i < session->workers().size(); ++i) {
     ModelSafeWorker* worker = work_session_->workers()[i];
     ModelSafeGroup group = worker->GetModelSafeGroup();
     // Skip workers whose group isn't active.
     if (groups_to_change.count(group) == 0u) {
       DVLOG(2) << "Skipping worker for group "
                << ModelSafeGroupToString(group);
       continue;
     }
 
     sessions::StatusController* status =
         work_session_->mutable_status_controller();
     sessions::ScopedModelSafeGroupRestriction r(status, group);
     WorkCallback c = base::Bind(
         &ModelChangingSyncerCommand::StartChangingModel,
         // We wait until the callback is executed. So it is safe to use
         // unretained.
         base::Unretained(this));
 
-    // TODO(lipalani): Check the return value for an unrecoverable error.
-    ignore_result(worker->DoWorkAndWaitUntilDone(c));
+    SyncerError this_worker_result = worker->DoWorkAndWaitUntilDone(c);
+    // TODO(rlarocque): Figure out a better way to deal with errors from
+    // multiple models at once.
+    if (this_worker_result != NO_ERROR)
+      result = this_worker_result;
+  }
 
-  }
+  return result;
 }
 
-bool ModelChangingSyncerCommand::ModelNeutralExecuteImpl(
+SyncerError ModelChangingSyncerCommand::ModelNeutralExecuteImpl(
     sessions::SyncSession* session) {
-  return true;
+  return NO_ERROR;
 }
 
 }  // namespace browser_sync