Pref service: Add initial support for pref registration.

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 d2dda357a2ff1162331ad7bac322835d82c0824e..a8fe15c70706d0a394fa15d3883790dead6cfa77 100644
--- a/services/preferences/public/cpp/persistent_pref_store_client.h
+++ b/services/preferences/public/cpp/persistent_pref_store_client.h
@@ -17,6 +17,8 @@ namespace base {
 class Value;
 }
 
+class PrefRegistry;
+
 namespace prefs {
 
 // An implementation of PersistentPrefStore backed by a
@@ -24,7 +26,8 @@ namespace prefs {
 class PersistentPrefStoreClient
     : public PrefStoreClientMixin<PersistentPrefStore> {
  public:
-  explicit PersistentPrefStoreClient(mojom::PrefStoreConnectorPtr connector);
+  PersistentPrefStoreClient(mojom::PrefStoreConnectorPtr connector,
+                            scoped_refptr<PrefRegistry> pref_registry);
 
   explicit PersistentPrefStoreClient(
       mojom::PersistentPrefStoreConnectionPtr connection);
@@ -60,6 +63,7 @@ class PersistentPrefStoreClient
                      other_pref_stores);
 
   mojom::PrefStoreConnectorPtr connector_;
+  scoped_refptr<PrefRegistry> pref_registry_;
   bool read_only_ = false;
   PrefReadError read_error_ = PersistentPrefStore::PREF_READ_ERROR_NONE;
   mojom::PersistentPrefStorePtr pref_store_;