[Sync] Fixing easy lint violations.

chrome/browser/sync/test/integration/migration_waiter.cc

 // Copyright 2014 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/test/integration/migration_waiter.h"
 
+#include <string>
+
 #include "base/logging.h"
 #include "chrome/browser/sync/test/integration/migration_watcher.h"
 
 MigrationWaiter::MigrationWaiter(syncer::ModelTypeSet expected_types,
                                  MigrationWatcher* watcher)
     : watcher_(watcher), expected_types_(expected_types) {
   DCHECK(!expected_types_.Empty());
   watcher_->set_migration_waiter(this);
 }
 
@@ skipping 10 matching lines @@
 
 std::string MigrationWaiter::GetDebugMessage() const {
   return "Waiting to migrate (" + ModelTypeSetToString(expected_types_) +
          "); " + "Currently migrated: (" +
          ModelTypeSetToString(watcher_->GetMigratedTypes()) + ")";
 }
 
 void MigrationWaiter::OnMigrationStateChange() {
   CheckExitCondition();
 }