Revert of Change base::Value::ListStorage to std::vector<base::Value>

components/ntp_snippets/pref_util.cc

Index: components/ntp_snippets/pref_util.cc
diff --git a/components/ntp_snippets/pref_util.cc b/components/ntp_snippets/pref_util.cc
index 3973cda1b1d53a01b50ae949675412d1c1eb5154..a6288f925356110976fab3ff423790530d283e11 100644
--- a/components/ntp_snippets/pref_util.cc
+++ b/components/ntp_snippets/pref_util.cc
@@ -16,9 +16,9 @@
                                                 const std::string& pref_name) {
   std::set<std::string> dismissed_ids;
   const base::ListValue* list = pref_service.GetList(pref_name);
-  for (const base::Value& value : *list) {
+  for (const std::unique_ptr<base::Value>& value : *list) {
     std::string dismissed_id;
-    bool success = value.GetAsString(&dismissed_id);
+    bool success = value->GetAsString(&dismissed_id);
     DCHECK(success) << "Failed to parse dismissed id from prefs param "
                     << pref_name << " into string.";
     dismissed_ids.insert(dismissed_id);