Run clang-modernize -use-nullptr over src/extensions/.

extensions/common/features/json_feature_provider_source.cc

Index: extensions/common/features/json_feature_provider_source.cc
diff --git a/extensions/common/features/json_feature_provider_source.cc b/extensions/common/features/json_feature_provider_source.cc
index 5b9ee168378f0ee4b719455f8337425c42e39591..db8ad98e363b9314cfd82dc1392d8053cdeaeacd 100644
--- a/extensions/common/features/json_feature_provider_source.cc
+++ b/extensions/common/features/json_feature_provider_source.cc
@@ -40,7 +40,7 @@ void JSONFeatureProviderSource::LoadJSON(int resource_id) {
   // Ensure there are no key collisions.
   for (base::DictionaryValue::Iterator iter(*value_as_dict); !iter.IsAtEnd();
        iter.Advance()) {
-    if (dictionary_.GetWithoutPathExpansion(iter.key(), NULL))
+    if (dictionary_.GetWithoutPathExpansion(iter.key(), nullptr))
       LOG(FATAL) << "Key " << iter.key() << " is defined in " << name_
                  << " JSON feature files more than once.";
   }