[ios] Add TODO to record usages of "return std::move(foo)" pattern.

ios/chrome/browser/share_extension/share_extension_service_factory.cc

 // Copyright 2016 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 "ios/chrome/browser/share_extension/share_extension_service_factory.h"
 
 #include "base/memory/singleton.h"
 #include "components/keyed_service/ios/browser_state_dependency_manager.h"
 #include "ios/chrome/browser/bookmarks/bookmark_model_factory.h"
 #include "ios/chrome/browser/browser_state/browser_state_otr_helper.h"
@@ skipping 32 matching lines @@
 
 std::unique_ptr<KeyedService>
 ShareExtensionServiceFactory::BuildServiceInstanceFor(
     web::BrowserState* context) const {
   ios::ChromeBrowserState* chrome_browser_state =
       ios::ChromeBrowserState::FromBrowserState(context);
   std::unique_ptr<ShareExtensionService> share_extension_service(
       new ShareExtensionService(
           ios::BookmarkModelFactory::GetForBrowserState(chrome_browser_state),
           ReadingListModelFactory::GetForBrowserState(chrome_browser_state)));
+  // TODO(crbug.com/703565): remove std::move() once Xcode 9.0+ is required.
   return std::move(share_extension_service);
 }
 
 web::BrowserState* ShareExtensionServiceFactory::GetBrowserStateToUse(
     web::BrowserState* context) const {
   return GetBrowserStateRedirectedInIncognito(context);
 }