Add presubmit check for scoped_ptr usage.

ui/app_list/search/history_data_store.cc

 // 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.
 
 #include "ui/app_list/search/history_data_store.h"
 
 #include "base/callback.h"
 #include "base/json/json_file_value_serializer.h"
 #include "base/json/json_string_value_serializer.h"
 #include "base/strings/string_number_conversions.h"
@@ skipping 41 matching lines @@
 //        "t" : "last_update_timestamp"
 //      },
 //      ...
 //    }
 //  }
 scoped_ptr<HistoryData::Associations> Parse(
     scoped_ptr<base::DictionaryValue> dict) {
   std::string version;
   if (!dict->GetStringWithoutPathExpansion(kKeyVersion, &version) ||
       version != kCurrentVersion) {
-    return scoped_ptr<HistoryData::Associations>();
+    return nullptr;
   }
 
   const base::DictionaryValue* assoc_dict = NULL;
   if (!dict->GetDictionaryWithoutPathExpansion(kKeyAssociations, &assoc_dict) ||
       !assoc_dict) {
-    return scoped_ptr<HistoryData::Associations>();
+    return nullptr;
   }
 
   scoped_ptr<HistoryData::Associations> data(new HistoryData::Associations);
   for (base::DictionaryValue::Iterator it(*assoc_dict); !it.IsAtEnd();
        it.Advance()) {
     const base::DictionaryValue* entry_dict = NULL;
     if (!it.value().GetAsDictionary(&entry_dict))
       continue;
 
     std::string primary;
@@ skipping 126 matching lines @@
     assoc_dict->SetWithoutPathExpansion(query, entry_dict);
   }
 
   return entry_dict;
 }
 
 void HistoryDataStore::OnDictionaryLoadedCallback(
     OnLoadedCallback callback,
     scoped_ptr<base::DictionaryValue> dict) {
   if (!dict) {
-    callback.Run(scoped_ptr<HistoryData::Associations>());
+    callback.Run(nullptr);
   } else {
     callback.Run(Parse(dict.Pass()).Pass());
   }
 }
 
 }  // namespace app_list