Pref service: Batch pref updates.

services/preferences/public/cpp/pref_store_client_mixin.h

Index: services/preferences/public/cpp/pref_store_client_mixin.h
diff --git a/services/preferences/public/cpp/pref_store_client_mixin.h b/services/preferences/public/cpp/pref_store_client_mixin.h
index 9d7a5080cb041b348a30ae535e1f51d01c1afdaa..19cf250c586ff1dfbe42c43cc300f21e52c1af00 100644
--- a/services/preferences/public/cpp/pref_store_client_mixin.h
+++ b/services/preferences/public/cpp/pref_store_client_mixin.h
@@ -54,10 +54,12 @@ class PrefStoreClientMixin : public BasePrefStore,
 
  private:
   // prefs::mojom::PreferenceObserver:
-  void OnPrefChanged(const std::string& key,
-                     std::unique_ptr<base::Value> value) override;
+  void OnPrefsChanged(std::vector<mojom::PrefUpdatePtr> updates) override;
   void OnInitializationCompleted(bool succeeded) override;
 
+  void OnPrefChanged(const std::string& key,
+                     std::unique_ptr<base::Value> value);
+
   // Cached preferences.
   // If null, indicates that initialization failed.
   std::unique_ptr<base::DictionaryValue> cached_prefs_;