Convert JsonWriter::Write to taking a const ref for the in-param

extensions/browser/value_store/leveldb_value_store.cc

Index: extensions/browser/value_store/leveldb_value_store.cc
diff --git a/extensions/browser/value_store/leveldb_value_store.cc b/extensions/browser/value_store/leveldb_value_store.cc
index ad8076dfdaf792193262e64504dbe918a16f2644..4b7d274edd13a9ec6160d5b07a0ca3f563a1f065 100644
--- a/extensions/browser/value_store/leveldb_value_store.cc
+++ b/extensions/browser/value_store/leveldb_value_store.cc
@@ -389,7 +389,7 @@ scoped_ptr<ValueStore::Error> LeveldbValueStore::AddToBatch(
 
   if (write_new_value) {
     std::string value_as_json;
-    if (!base::JSONWriter::Write(&value, &value_as_json))
+    if (!base::JSONWriter::Write(value, &value_as_json))
       return Error::Create(OTHER_ERROR, kCannotSerialize, util::NewKey(key));
     batch->Put(key, value_as_json);
   }