Add a TODO for crbug/703565

ios/web_view/internal/translate/web_view_translate_ranker_factory.cc

 // Copyright 2017 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/web_view/internal/translate/web_view_translate_ranker_factory.h"
 
 #include <utility>
 
 #include "base/memory/ptr_util.h"
 #include "base/memory/singleton.h"
@@ skipping 29 matching lines @@
     web::BrowserState* context) const {
   WebViewBrowserState* web_view_browser_state =
       WebViewBrowserState::FromBrowserState(context);
   std::unique_ptr<translate::TranslateRankerImpl> ranker =
       base::MakeUnique<translate::TranslateRankerImpl>(
           translate::TranslateRankerImpl::GetModelPath(
               web_view_browser_state->GetStatePath()),
           translate::TranslateRankerImpl::GetModelURL());
   // WebView has no consumer of translate ranker events, so don't generate them.
   ranker->EnableLogging(false);
-  return std::move(ranker);  // Fails xcode-clang compile without the move.
+
+  // TODO(crbug.com/703565): remove std::move() once Xcode 9.0+ is required.
+  return std::move(ranker);
 }
 
 }  // namespace ios_web_view