Pref service: have Mash and Chrome connect to the right pref stores

services/preferences/public/interfaces/preferences.mojom

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 module prefs.mojom;
 
 import "mojo/common/values.mojom";
 import "services/preferences/public/interfaces/preferences_configuration.mojom";
 
 const string kServiceName = "preferences";
@@ skipping 72 matching lines @@
 // connected to through the |PrefStoreConnector| interface.
 interface PrefStoreRegistry {
   // Register a pref store.
   Register(PrefStoreType type, PrefStore pref_store);
 };
 
 // Allows connections to pref stores registered with |PrefStoreRegistry|.
 interface PrefStoreConnector {
   // Connect to all registered pref stores, retrieving the current values of all
   // prefs in each store and an |observer| interfaces through which updates can
-  // be received.
+  // be received. The client asserts that it is already connected to the
+  // |already_connected_types| pref stores through some other means, so the
+  // Connect call will not connect to those.
   [Sync]
-  Connect(PrefRegistry pref_registry) =>
+  Connect(PrefRegistry pref_registry,
+          array<PrefStoreType> already_connected_types) =>
       (PersistentPrefStoreConnection connection,
        map<PrefStoreType, PrefStoreConnection> connections);
 };
 
 // An interface providing mutation access to a PersistentPrefStore.
 interface PersistentPrefStore {
   // Sets the value for |key|. A null |value| indicates a delete. |flags| is a
   // bitmask of WritablePrefStore::PrefWriteFlags.
   SetValue(string key, mojo.common.mojom.Value? value, uint32 flags);
 
@@ skipping 15 matching lines @@
   // PrefRegistry::PrefRegistrationFlags and
   // PrefRegistrySyncable::PrefRegistrationFlags.
   uint32 flags;
 };
 
 interface PrefServiceControl {
   // Initializes the pref service. This must be called before the service can
   // be used.
   Init(PersistentPrefStoreConfiguration configuration);
 };