buffet: StorageInterface::Save accepts const reference

Out codebase mostly written with assumption that const parameters
passed as const reference.
Looking at storage_->Save(&dict) reader may believe that dict is the
destination for Save.

BUG=none
TEST=gizmo-emerge buffet

Change-Id: I15b2b1a48e3053979ecd28a8e8775997e7b7e06d
Reviewed-on: https://chromium-review.googlesource.com/270793
Commit-Queue: Vitaly Buka <vitalybuka@chromium.org>
Tested-by: Vitaly Buka <vitalybuka@chromium.org>
Reviewed-by: Alex Vakulenko <avakulenko@chromium.org>
diff --git a/buffet/storage_impls.cc b/buffet/storage_impls.cc
index d95538a..e45ddbf 100644
--- a/buffet/storage_impls.cc
+++ b/buffet/storage_impls.cc
@@ -23,10 +23,10 @@
   return std::unique_ptr<base::Value>(base::JSONReader::Read(json));
 }
 
-bool FileStorage::Save(const base::Value* config) {
+bool FileStorage::Save(const base::Value& config) {
   std::string json;
   base::JSONWriter::WriteWithOptions(
-      config, base::JSONWriter::OPTIONS_PRETTY_PRINT, &json);
+      &config, base::JSONWriter::OPTIONS_PRETTY_PRINT, &json);
   return base::ImportantFileWriter::WriteFileAtomically(file_path_, json);
 }
 
@@ -35,8 +35,8 @@
   return std::unique_ptr<base::Value>(cache_->DeepCopy());
 }
 
-bool MemStorage::Save(const base::Value* config) {
-  cache_.reset(config->DeepCopy());
+bool MemStorage::Save(const base::Value& config) {
+  cache_.reset(config.DeepCopy());
   ++save_count_;
   return true;
 }