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

ios/web/web_state/web_state_impl.mm

 // Copyright 2013 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.
 
 #import "ios/web/web_state/web_state_impl.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include "base/logging.h"
@@ skipping 30 matching lines @@
 
 namespace web {
 
 /* static */
 std::unique_ptr<WebState> WebState::Create(const CreateParams& params) {
   std::unique_ptr<WebStateImpl> web_state(new WebStateImpl(params));
 
   // Initialize the new session.
   web_state->GetNavigationManagerImpl().InitializeSession();
 
-  // This std::move is required to compile with the version of clang shipping
-  // with Xcode 8.0+. Evalute whether the issue is fixed once a new version of
-  // Xcode is released.
+  // TODO(crbug.com/703565): remove std::move() once Xcode 9.0+ is required.
   return std::move(web_state);
 }
 
 /* static */
 std::unique_ptr<WebState> WebState::Create(const CreateParams& params,
                                            CRWSessionStorage* session_storage) {
   std::unique_ptr<WebStateImpl> web_state(
       new WebStateImpl(params, session_storage));
 
-  // This std::move is required to compile with the version of clang shipping
-  // with Xcode 8.0+. Evalute whether the issue is fixed once a new version of
-  // Xcode is released.
+  // TODO(crbug.com/703565): remove std::move() once Xcode 9.0+ is required.
   return std::move(web_state);
 }
 
 WebStateImpl::WebStateImpl(const CreateParams& params)
     : WebStateImpl(params, nullptr) {}
 
 WebStateImpl::WebStateImpl(const CreateParams& params,
                            CRWSessionStorage* session_storage)
     : delegate_(nullptr),
       is_loading_(false),
@@ skipping 688 matching lines @@
     const LoadCommittedDetails& load_details) {
   for (auto& observer : observers_)
     observer.NavigationItemCommitted(load_details);
 }
 
 WebState* WebStateImpl::GetWebState() {
   return this;
 }
 
 }  // namespace web