diff -r 000000000000 -r 6474c204b198 mobile/android/modules/SharedPreferences.jsm
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mobile/android/modules/SharedPreferences.jsm	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,198 @@
+// -*- Mode: js2; tab-width: 2; indent-tabs-mode: nil; js2-basic-offset: 2; js2-skip-preprocessor-directives: t; -*-
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+this.EXPORTED_SYMBOLS = ["SharedPreferences"];
+
+const { classes: Cc, interfaces: Ci, utils: Cu } = Components;
+
+// For adding observers.
+Cu.import("resource://gre/modules/Services.jsm");
+Cu.import("resource://gre/modules/Messaging.jsm");
+
+/**
+ * Create an interface to an Android SharedPreferences branch.
+ *
+ * branch {String} should be a string describing a preferences branch,
+ * like "UpdateService" or "background.data", or null to access the
+ * default preferences branch for the application.
+ */
+function SharedPreferences(branch) {
+  if (!(this instanceof SharedPreferences)) {
+    return new SharedPreferences(branch);
+  }
+  this._branch = branch || null;
+  this._observers = {};
+};
+
+SharedPreferences.prototype = Object.freeze({
+  _set: function _set(prefs) {
+    sendMessageToJava({
+      type: "SharedPreferences:Set",
+      preferences: prefs,
+      branch: this._branch,
+    });
+  },
+
+  _setOne: function _setOne(prefName, value, type) {
+    let prefs = [];
+    prefs.push({
+      name: prefName,
+      value: value,
+      type: type,
+    });
+    this._set(prefs);
+  },
+
+  setBoolPref: function setBoolPref(prefName, value) {
+    this._setOne(prefName, value, "bool");
+  },
+
+  setCharPref: function setCharPref(prefName, value) {
+    this._setOne(prefName, value, "string");
+  },
+
+  setIntPref: function setIntPref(prefName, value) {
+    this._setOne(prefName, value, "int");
+  },
+
+  _get: function _get(prefs, callback) {
+    let result = null;
+    sendMessageToJava({
+      type: "SharedPreferences:Get",
+      preferences: prefs,
+      branch: this._branch,
+    }, (data) => {
+      result = data.values;
+    });
+
+    let thread = Services.tm.currentThread;
+    while (result == null)
+      thread.processNextEvent(true);
+
+    return result;
+  },
+
+  _getOne: function _getOne(prefName, type) {
+    let prefs = [];
+    prefs.push({
+      name: prefName,
+      type: type,
+    });
+    let values = this._get(prefs);
+    if (values.length != 1) {
+      throw new Error("Got too many values: " + values.length);
+    }
+    return values[0].value;
+  },
+
+  getBoolPref: function getBoolPref(prefName) {
+    return this._getOne(prefName, "bool");
+  },
+
+  getCharPref: function getCharPref(prefName) {
+    return this._getOne(prefName, "string");
+  },
+
+  getIntPref: function getIntPref(prefName) {
+    return this._getOne(prefName, "int");
+  },
+
+  /**
+   * Invoke `observer` after a change to the preference `domain` in
+   * the current branch.
+   *
+   * `observer` should implement the nsIObserver.observe interface.
+   */
+  addObserver: function addObserver(domain, observer, holdWeak) {
+    if (!domain)
+      throw new Error("domain must not be null");
+    if (!observer)
+      throw new Error("observer must not be null");
+    if (holdWeak)
+      throw new Error("Weak references not yet implemented.");
+
+    if (!this._observers.hasOwnProperty(domain))
+      this._observers[domain] = [];
+    if (this._observers[domain].indexOf(observer) > -1)
+      return;
+
+    this._observers[domain].push(observer);
+
+    this._updateAndroidListener();
+  },
+
+  /**
+   * Do not invoke `observer` after a change to the preference
+   * `domain` in the current branch.
+   */
+  removeObserver: function removeObserver(domain, observer) {
+    if (!this._observers.hasOwnProperty(domain))
+      return;
+    let index = this._observers[domain].indexOf(observer);
+    if (index < 0)
+      return;
+
+    this._observers[domain].splice(index, 1);
+    if (this._observers[domain].length < 1)
+      delete this._observers[domain];
+
+    this._updateAndroidListener();
+  },
+
+  _updateAndroidListener: function _updateAndroidListener() {
+    if (this._listening && Object.keys(this._observers).length < 1)
+      this._uninstallAndroidListener();
+    if (!this._listening && Object.keys(this._observers).length > 0)
+      this._installAndroidListener();
+  },
+
+  _installAndroidListener: function _installAndroidListener() {
+    if (this._listening)
+      return;
+    this._listening = true;
+
+    Services.obs.addObserver(this, "SharedPreferences:Changed", false);
+    sendMessageToJava({
+      type: "SharedPreferences:Observe",
+      enable: true,
+      branch: this._branch,
+    });
+  },
+
+  observe: function observe(subject, topic, data) {
+    if (topic != "SharedPreferences:Changed") {
+      return;
+    }
+
+    let msg = JSON.parse(data);
+    if (msg.branch != this._branch) {
+      return;
+    }
+
+    if (!this._observers.hasOwnProperty(msg.key)) {
+      return;
+    }
+
+    let observers = this._observers[msg.key];
+    for (let obs of observers) {
+      obs.observe(obs, msg.key, msg.value);
+    }
+  },
+
+  _uninstallAndroidListener: function _uninstallAndroidListener() {
+    if (!this._listening)
+      return;
+    this._listening = false;
+
+    Services.obs.removeObserver(this, "SharedPreferences:Changed");
+    sendMessageToJava({
+      type: "SharedPreferences:Observe",
+      enable: false,
+      branch: this._branch,
+    });
+  },
+});