Chrome Version: ToT
OS: All

|WriteablePrefStore::SetValue| should return |base::Value*| to avoid double lookup when we want to keep a pointer into the pref store. Counting that raw pointer value passed to |SetValue| will remain valid is ungrounded.

|PrefValueMap::SetValue| should probably also return |base::Value*| but there it is complicated by the fact that it already returns |bool| (whether the value is different from the previous one) which is used in a few callers to avoid notifying observers when no actual change happened.