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

components/password_manager/core/browser/form_fetcher_impl.cc

Index: components/password_manager/core/browser/form_fetcher_impl.cc
diff --git a/components/password_manager/core/browser/form_fetcher_impl.cc b/components/password_manager/core/browser/form_fetcher_impl.cc
index 789180a975a75faba54009c2c9a1ff237ad02660..c4f922c5a11e02c5924dea796a3d3185b700717d 100644
--- a/components/password_manager/core/browser/form_fetcher_impl.cc
+++ b/components/password_manager/core/browser/form_fetcher_impl.cc
@@ -201,7 +201,7 @@ std::unique_ptr<FormFetcher> FormFetcherImpl::Clone() {
   result->state_ = this->state_;
   result->need_to_refetch_ = this->need_to_refetch_;
 
-  // Move needed for upcasting.
+  // TODO(crbug.com/703565): remove std::move() once Xcode 9.0+ is required.
   return std::move(result);
 }