Implement lossy pref behavior for JsonPrefStore.

ui/app_list/search/dictionary_data_store.cc

Index: ui/app_list/search/dictionary_data_store.cc
diff --git a/ui/app_list/search/dictionary_data_store.cc b/ui/app_list/search/dictionary_data_store.cc
index 45f53ca6edb58101530b4cc03cf1e5416218c06c..33e17e331e93e901c451b0bfd71c81436b5c85e5 100644
--- a/ui/app_list/search/dictionary_data_store.cc
+++ b/ui/app_list/search/dictionary_data_store.cc
@@ -5,6 +5,7 @@
 #include "ui/app_list/search/dictionary_data_store.h"
 
 #include "base/callback.h"
+#include "base/files/important_file_writer.h"
 #include "base/json/json_file_value_serializer.h"
 #include "base/json/json_string_value_serializer.h"
 #include "base/logging.h"
@@ -28,7 +29,7 @@ DictionaryDataStore::DictionaryDataStore(const base::FilePath& data_file,
       worker_pool->GetNamedSequenceToken(token),
       base::SequencedWorkerPool::SKIP_ON_SHUTDOWN);
   writer_.reset(
-      new base::ImportantFileWriter(data_file, file_task_runner_.get()));
+      new base::ImportantFileWriterImpl(data_file, file_task_runner_.get()));
 
   cached_dict_.reset(new base::DictionaryValue);
 }