Add struct traits for base::Value.

services/preferences/public/cpp/pref_observer_store.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "services/preferences/public/cpp/pref_observer_store.h"
 
 #include "base/values.h"
 #include "mojo/public/cpp/bindings/array.h"
 #include "services/service_manager/public/cpp/connector.h"
 
@@ skipping 60 matching lines @@
   ValueMapPrefStore::SetValueSilently(key, std::move(value), flags);
 }
 
 PrefObserverStore::~PrefObserverStore() {}
 
 void PrefObserverStore::SetValueOnPreferenceManager(const std::string& key,
                                                     const base::Value& value) {
   if (keys_.find(key) == keys_.end())
     return;
 
-  base::DictionaryValue prefs;
-  prefs.Set(key, value.CreateDeepCopy());
-  prefs_manager_ptr_->SetPreferences(prefs);
+  auto prefs = base::MakeUnique<base::DictionaryValue>();
+  prefs->Set(key, value.CreateDeepCopy());
+  prefs_manager_ptr_->SetPreferences(std::move(prefs));
 }
 
 void PrefObserverStore::OnPreferencesChanged(
-    const base::DictionaryValue& preferences) {
-  for (base::DictionaryValue::Iterator it(preferences); !it.IsAtEnd();
+    std::unique_ptr<base::DictionaryValue> preferences) {
+  for (base::DictionaryValue::Iterator it(*preferences); !it.IsAtEnd();
        it.Advance()) {
     if (keys_.find(it.key()) == keys_.end())
       continue;
     // We deliberately call the parent to avoid notifying the server again.
     ValueMapPrefStore::SetValue(it.key(), it.value().CreateDeepCopy(), 0);
   }
 
   if (!initialized_) {
     initialized_ = true;
     NotifyInitializationCompleted();
   }
 }