Pref service: add persistent pref store frontend and backend.

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";
 
 const string kServiceName = "preferences";
 
@@ skipping 73 matching lines @@
   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.
   Connect() => (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);
+
+  // These mirror the C++ PersistentPrefStore methods.
+  CommitPendingWrite();
+  SchedulePendingLossyWrites();
+  ClearMutableValues();
+};
+
+// A connector that provides a way to connect to a PersistentPrefStore.
+interface PersistentPrefStoreConnector {
+  enum ReadError {
+    NONE = 0,
+    JSON_PARSE = 1,
+    JSON_TYPE = 2,
+    ACCESS_DENIED = 3,
+    FILE_OTHER = 4,
+    FILE_LOCKED = 5,
+    NO_FILE = 6,
+    JSON_REPEAT = 7,
+    // OTHER = 8,  // Deprecated.
+    FILE_NOT_SPECIFIED = 9,
+    ASYNCHRONOUS_TASK_INCOMPLETE = 10,
+  };
+
+  // Connects to the PersistentPrefStore.
+  // A null |preferences| indicates that the pref service failed to load prefs.
+  // |pref_store| provides write access; |observer| is used to observe writes
+  // instigated by other clients.
+  [Sync]
+  Connect() => (
+      ReadError read_error,
+      bool read_only,
+      mojo.common.mojom.DictionaryValue? preferences,
+      PersistentPrefStore? pref_store,
+      PrefStoreObserver&? observer);
+};