Pref service: Batch pref updates.

services/preferences/public/cpp/persistent_pref_store_client.h

Index: services/preferences/public/cpp/persistent_pref_store_client.h
diff --git a/services/preferences/public/cpp/persistent_pref_store_client.h b/services/preferences/public/cpp/persistent_pref_store_client.h
index 6ed2b1164d71e2d3ea4896648d1b79d822779db3..e317ec9f163d54c39e6d7757ee14ca9249a00c1f 100644
--- a/services/preferences/public/cpp/persistent_pref_store_client.h
+++ b/services/preferences/public/cpp/persistent_pref_store_client.h
@@ -66,15 +66,21 @@ class PersistentPrefStoreClient
                                     prefs::mojom::PrefStoreConnectionPtr>
                      other_pref_stores);
 
+  void QueueWrite(const std::string& key, uint32_t flags);
+  void FlushPendingWrites();
+
   mojom::PrefStoreConnectorPtr connector_;
   scoped_refptr<PrefRegistry> pref_registry_;
   bool read_only_ = false;
   PrefReadError read_error_ = PersistentPrefStore::PREF_READ_ERROR_NONE;
   mojom::PersistentPrefStorePtr pref_store_;
+  std::map<std::string, uint32_t> pending_writes_;
 
   std::unique_ptr<ReadErrorDelegate> error_delegate_;
   std::vector<PrefValueStore::PrefStoreType> already_connected_types_;
 
+  base::WeakPtrFactory<PersistentPrefStoreClient> weak_factory_;
+
   DISALLOW_COPY_AND_ASSIGN(PersistentPrefStoreClient);
 };