Pref service: Add a ScopedDictionaryPrefUpdate to track value changes.

services/preferences/public/cpp/tests/pref_store_client_unittest.cc

Index: services/preferences/public/cpp/tests/pref_store_client_unittest.cc
diff --git a/services/preferences/public/cpp/tests/pref_store_client_unittest.cc b/services/preferences/public/cpp/tests/pref_store_client_unittest.cc
index dbf86d41650d6a7ab3255e6567dc9738dfa4583a..8952cbf5c936fbead3d1856bf44013664f10e225 100644
--- a/services/preferences/public/cpp/tests/pref_store_client_unittest.cc
+++ b/services/preferences/public/cpp/tests/pref_store_client_unittest.cc
@@ -41,7 +41,9 @@ class PrefStoreClientTest : public testing::Test {
   bool initialized() { return store_->IsInitializationComplete(); }
   void OnPrefChanged(const std::string& key, const base::Value& value) {
     std::vector<mojom::PrefUpdatePtr> updates;
-    updates.push_back(mojom::PrefUpdate::New(key, value.CreateDeepCopy(), 0));
+    updates.push_back(mojom::PrefUpdate::New(
+        key, mojom::PrefUpdateValue::NewAtomicUpdate(value.CreateDeepCopy()),
+        0));
     observer_ptr_->OnPrefsChanged(std::move(updates));
   }
   void OnInitializationCompleted() {