[ios] Fixed memory management bug in TestJavaScriptDialogPresenter.

ios/web/public/test/fakes/test_java_script_dialog_presenter.mm

Index: ios/web/public/test/fakes/test_java_script_dialog_presenter.mm
diff --git a/ios/web/public/test/fakes/test_java_script_dialog_presenter.mm b/ios/web/public/test/fakes/test_java_script_dialog_presenter.mm
index c0bb09f221c9d3c0d5b830e891fba1af67913148..2e44213214ba5c60c015893fa12fc6e03d199ed6 100644
--- a/ios/web/public/test/fakes/test_java_script_dialog_presenter.mm
+++ b/ios/web/public/test/fakes/test_java_script_dialog_presenter.mm
@@ -28,8 +28,8 @@ void TestJavaScriptDialogPresenter::RunJavaScriptDialog(
   dialog.web_state = web_state;
   dialog.origin_url = origin_url;
   dialog.java_script_dialog_type = java_script_dialog_type;
-  dialog.message_text.reset(message_text);
-  dialog.default_prompt_text.reset(default_prompt_text);
+  dialog.message_text.reset([message_text copy]);
+  dialog.default_prompt_text.reset([default_prompt_text copy]);
 
   requested_dialogs_.push_back(dialog);