Pref service: integrate PersistentPrefStoreImpl with PrefStoreManagerImpl.

services/preferences/public/interfaces/preferences.mojom

Index: services/preferences/public/interfaces/preferences.mojom
diff --git a/services/preferences/public/interfaces/preferences.mojom b/services/preferences/public/interfaces/preferences.mojom
index 23a2010e225bbb7b4773630da07ab7781cd39f1c..d4258981749eb1bb4974f147d73ac7bf5ecb61b9 100644
--- a/services/preferences/public/interfaces/preferences.mojom
+++ b/services/preferences/public/interfaces/preferences.mojom
@@ -5,6 +5,7 @@
 module prefs.mojom;
 
 import "mojo/common/values.mojom";
+import "services/preferences/public/interfaces/preferences_configuration.mojom";
 
 const string kServiceName = "preferences";
 
@@ -132,3 +133,9 @@ interface PersistentPrefStoreConnector {
       PersistentPrefStore? pref_store,
       PrefStoreObserver&? observer);
 };
+
+interface PrefServiceControl {
+  // Initializes the pref service. This must be called before the service can
+  // be used.
+  Init(PersistentPrefStoreConfiguration configuration);
+};