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diff --git a/components/downloads/DownloadsCommon.jsm b/components/downloads/DownloadsCommon.jsm
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=2 et sw=2 tw=80 filetype=javascript: */
+/* 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 = [
+  "DownloadsCommon",
+];
+
+/**
+ * Handles the Downloads panel shared methods and data access.
+ *
+ * This file includes the following constructors and global objects:
+ *
+ * DownloadsCommon
+ * This object is exposed directly to the consumers of this JavaScript module,
+ * and provides shared methods for all the instances of the user interface.
+ *
+ * DownloadsData
+ * Retrieves the list of past and completed downloads from the underlying
+ * Downloads API data, and provides asynchronous notifications allowing
+ * to build a consistent view of the available data.
+ *
+ * DownloadsIndicatorData
+ * This object registers itself with DownloadsData as a view, and transforms the
+ * notifications it receives into overall status data, that is then broadcast to
+ * the registered download status indicators.
+ */
+
+////////////////////////////////////////////////////////////////////////////////
+//// Globals
+
+const Cc = Components.classes;
+const Ci = Components.interfaces;
+const Cu = Components.utils;
+const Cr = Components.results;
+
+Cu.import("resource://gre/modules/XPCOMUtils.jsm");
+Cu.import("resource://gre/modules/Services.jsm");
+
+XPCOMUtils.defineLazyModuleGetter(this, "NetUtil",
+                                  "resource://gre/modules/NetUtil.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "PluralForm",
+                                  "resource://gre/modules/PluralForm.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "Downloads",
+                                  "resource://gre/modules/Downloads.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "DownloadUIHelper",
+                                  "resource://gre/modules/DownloadUIHelper.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "DownloadUtils",
+                                  "resource://gre/modules/DownloadUtils.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "FileUtils",
+                                  "resource://gre/modules/FileUtils.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "OS",
+                                  "resource://gre/modules/osfile.jsm")
+XPCOMUtils.defineLazyModuleGetter(this, "PlacesUtils",
+                                  "resource://gre/modules/PlacesUtils.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "PrivateBrowsingUtils",
+                                  "resource://gre/modules/PrivateBrowsingUtils.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "RecentWindow",
+                                  "resource:///modules/RecentWindow.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "PlacesUtils",
+                                  "resource://gre/modules/PlacesUtils.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "Promise",
+                                  "resource://gre/modules/Promise.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "DownloadsLogger",
+                                  "resource:///modules/DownloadsLogger.jsm");
+
+const nsIDM = Ci.nsIDownloadManager;
+
+const kDownloadsStringBundleUrl =
+  "chrome://browser/locale/downloads/downloads.properties";
+
+const kPrefConfirmOpenExe = "browser.download.confirmOpenExecutable";
+
+const kDownloadsStringsRequiringFormatting = {
+  sizeWithUnits: true,
+  shortTimeLeftSeconds: true,
+  shortTimeLeftMinutes: true,
+  shortTimeLeftHours: true,
+  shortTimeLeftDays: true,
+  statusSeparator: true,
+  statusSeparatorBeforeNumber: true,
+  fileExecutableSecurityWarning: true
+};
+
+const kDownloadsStringsRequiringPluralForm = {
+  otherDownloads2: true
+};
+
+const kPartialDownloadSuffix = ".part";
+
+const kPrefBranch = Services.prefs.getBranch("browser.download.");
+
+var PrefObserver = {
+  QueryInterface: XPCOMUtils.generateQI([Ci.nsIObserver,
+                                         Ci.nsISupportsWeakReference]),
+  getPref: function PO_getPref(name) {
+    try {
+      switch (typeof this.prefs[name]) {
+        case "boolean":
+          return kPrefBranch.getBoolPref(name);
+      }
+    } catch (ex) { }
+    return this.prefs[name];
+  },
+  observe: function PO_observe(aSubject, aTopic, aData) {
+    if (this.prefs.hasOwnProperty(aData)) {
+      return this[aData] = this.getPref(aData);
+    }
+  },
+  register: function PO_register(prefs) {
+    this.prefs = prefs;
+    kPrefBranch.addObserver("", this, true);
+    for (let key in prefs) {
+      let name = key;
+      XPCOMUtils.defineLazyGetter(this, name, function () {
+        return PrefObserver.getPref(name);
+      });
+    }
+  },
+};
+
+PrefObserver.register({
+  // prefName: defaultValue
+  debug: false,
+  animateNotifications: true
+});
+
+
+////////////////////////////////////////////////////////////////////////////////
+//// DownloadsCommon
+
+/**
+ * This object is exposed directly to the consumers of this JavaScript module,
+ * and provides shared methods for all the instances of the user interface.
+ */
+this.DownloadsCommon = {
+  log: function DC_log(...aMessageArgs) {
+    delete this.log;
+    this.log = function DC_log(...aMessageArgs) {
+      if (!PrefObserver.debug) {
+        return;
+      }
+      DownloadsLogger.log.apply(DownloadsLogger, aMessageArgs);
+    }
+    this.log.apply(this, aMessageArgs);
+  },
+
+  error: function DC_error(...aMessageArgs) {
+    delete this.error;
+    this.error = function DC_error(...aMessageArgs) {
+      if (!PrefObserver.debug) {
+        return;
+      }
+      DownloadsLogger.reportError.apply(DownloadsLogger, aMessageArgs);
+    }
+    this.error.apply(this, aMessageArgs);
+  },
+  /**
+   * Returns an object whose keys are the string names from the downloads string
+   * bundle, and whose values are either the translated strings or functions
+   * returning formatted strings.
+   */
+  get strings()
+  {
+    let strings = {};
+    let sb = Services.strings.createBundle(kDownloadsStringBundleUrl);
+    let enumerator = sb.getSimpleEnumeration();
+    while (enumerator.hasMoreElements()) {
+      let string = enumerator.getNext().QueryInterface(Ci.nsIPropertyElement);
+      let stringName = string.key;
+      if (stringName in kDownloadsStringsRequiringFormatting) {
+        strings[stringName] = function () {
+          // Convert "arguments" to a real array before calling into XPCOM.
+          return sb.formatStringFromName(stringName,
+                                         Array.slice(arguments, 0),
+                                         arguments.length);
+        };
+      } else if (stringName in kDownloadsStringsRequiringPluralForm) {
+        strings[stringName] = function (aCount) {
+          // Convert "arguments" to a real array before calling into XPCOM.
+          let formattedString = sb.formatStringFromName(stringName,
+                                         Array.slice(arguments, 0),
+                                         arguments.length);
+          return PluralForm.get(aCount, formattedString);
+        };
+      } else {
+        strings[stringName] = string.value;
+      }
+    }
+    delete this.strings;
+    return this.strings = strings;
+  },
+
+  /**
+   * Generates a very short string representing the given time left.
+   *
+   * @param aSeconds
+   *        Value to be formatted.  It represents the number of seconds, it must
+   *        be positive but does not need to be an integer.
+   *
+   * @return Formatted string, for example "30s" or "2h".  The returned value is
+   *         maximum three characters long, at least in English.
+   */
+  formatTimeLeft: function DC_formatTimeLeft(aSeconds)
+  {
+    // Decide what text to show for the time
+    let seconds = Math.round(aSeconds);
+    if (!seconds) {
+      return "";
+    } else if (seconds <= 30) {
+      return DownloadsCommon.strings["shortTimeLeftSeconds"](seconds);
+    }
+    let minutes = Math.round(aSeconds / 60);
+    if (minutes < 60) {
+      return DownloadsCommon.strings["shortTimeLeftMinutes"](minutes);
+    }
+    let hours = Math.round(minutes / 60);
+    if (hours < 48) { // two days
+      return DownloadsCommon.strings["shortTimeLeftHours"](hours);
+    }
+    let days = Math.round(hours / 24);
+    return DownloadsCommon.strings["shortTimeLeftDays"](Math.min(days, 99));
+  },
+
+  /**
+   * Indicates whether we should show the full Download Manager window interface
+   * instead of the simplified panel interface.  The behavior of downloads
+   * across browsing session is consistent with the selected interface.
+   */
+  get useToolkitUI()
+  {
+    /* Toolkit UI is currently incompatible.
+     * FIXME: Either fix the toolkitUI (make DBConnection work) or remove
+     * the unused code altogether
+     */
+    //try {
+    //  return Services.prefs.getBoolPref("browser.download.useToolkitUI");
+    //} catch (ex) { }
+    return false;
+  },
+
+  /**
+   * Indicates whether we should show visual notification on the indicator
+   * when a download event is triggered.
+   */
+  get animateNotifications()
+  {
+    return PrefObserver.animateNotifications;
+  },
+
+  /**
+   * Get access to one of the DownloadsData or PrivateDownloadsData objects,
+   * depending on the privacy status of the window in question.
+   *
+   * @param aWindow
+   *        The browser window which owns the download button.
+   */
+  getData: function DC_getData(aWindow) {
+    if (PrivateBrowsingUtils.isWindowPrivate(aWindow)) {
+      return PrivateDownloadsData;
+    } else {
+      return DownloadsData;
+    }
+  },
+
+  /**
+   * Initializes the data link for both the private and non-private downloads
+   * data objects.
+   *
+   * @param aDownloadManagerService
+   *        Reference to the service implementing nsIDownloadManager.  We need
+   *        this because getService isn't available for us when this method is
+   *        called, and we must ensure to register our listeners before the
+   *        getService call for the Download Manager returns.
+   */
+  initializeAllDataLinks: function DC_initializeAllDataLinks(aDownloadManagerService) {
+    DownloadsData.initializeDataLink(aDownloadManagerService);
+    PrivateDownloadsData.initializeDataLink(aDownloadManagerService);
+  },
+
+  /**
+   * Terminates the data link for both the private and non-private downloads
+   * data objects.
+   */
+  terminateAllDataLinks: function DC_terminateAllDataLinks() {
+    DownloadsData.terminateDataLink();
+    PrivateDownloadsData.terminateDataLink();
+  },
+
+  /**
+   * Reloads the specified kind of downloads from the non-private store.
+   * This method must only be called when Private Browsing Mode is disabled.
+   *
+   * @param aActiveOnly
+   *        True to load only active downloads from the database.
+   */
+  ensureAllPersistentDataLoaded:
+  function DC_ensureAllPersistentDataLoaded(aActiveOnly) {
+    DownloadsData.ensurePersistentDataLoaded(aActiveOnly);
+  },
+
+  /**
+   * Get access to one of the DownloadsIndicatorData or
+   * PrivateDownloadsIndicatorData objects, depending on the privacy status of
+   * the window in question.
+   */
+  getIndicatorData: function DC_getIndicatorData(aWindow) {
+    if (PrivateBrowsingUtils.isWindowPrivate(aWindow)) {
+      return PrivateDownloadsIndicatorData;
+    } else {
+      return DownloadsIndicatorData;
+    }
+  },
+
+  /**
+   * Returns a reference to the DownloadsSummaryData singleton - creating one
+   * in the process if one hasn't been instantiated yet.
+   *
+   * @param aWindow
+   *        The browser window which owns the download button.
+   * @param aNumToExclude
+   *        The number of items on the top of the downloads list to exclude
+   *        from the summary.
+   */
+  getSummary: function DC_getSummary(aWindow, aNumToExclude)
+  {
+    if (PrivateBrowsingUtils.isWindowPrivate(aWindow)) {
+      if (this._privateSummary) {
+        return this._privateSummary;
+      }
+      return this._privateSummary = new DownloadsSummaryData(true, aNumToExclude);
+    } else {
+      if (this._summary) {
+        return this._summary;
+      }
+      return this._summary = new DownloadsSummaryData(false, aNumToExclude);
+    }
+  },
+  _summary: null,
+  _privateSummary: null,
+
+  /**
+   * Returns the legacy state integer value for the provided Download object.
+   */
+  stateOfDownload(download) {
+    // Collapse state using the correct priority.
+    if (!download.stopped) {
+      return nsIDM.DOWNLOAD_DOWNLOADING;
+    }
+    if (download.succeeded) {
+      return nsIDM.DOWNLOAD_FINISHED;
+    }
+    if (download.error) {
+      if (download.error.becauseBlockedByParentalControls) {
+        return nsIDM.DOWNLOAD_BLOCKED_PARENTAL;
+      }
+      if (download.error.becauseBlockedByReputationCheck) {
+        return nsIDM.DOWNLOAD_DIRTY;
+      }
+      return nsIDM.DOWNLOAD_FAILED;
+    }
+    if (download.canceled) {
+      if (download.hasPartialData) {
+        return nsIDM.DOWNLOAD_PAUSED;
+      }
+      return nsIDM.DOWNLOAD_CANCELED;
+    }
+    return nsIDM.DOWNLOAD_NOTSTARTED;
+  },
+
+  /**
+   * Helper function required because the Downloads Panel and the Downloads View
+   * don't share the controller yet.
+   */
+  removeAndFinalizeDownload(download) {
+    Downloads.getList(Downloads.ALL)
+             .then(list => list.remove(download))
+             .then(() => download.finalize(true))
+             .catch(Cu.reportError);
+  },
+
+  /**
+   * Given an iterable collection of Download objects, generates and returns
+   * statistics about that collection.
+   *
+   * @param downloads An iterable collection of Download objects.
+   *
+   * @return Object whose properties are the generated statistics. Currently,
+   *         we return the following properties:
+   *
+   *         numActive       : The total number of downloads.
+   *         numPaused       : The total number of paused downloads.
+   *         numDownloading  : The total number of downloads being downloaded.
+   *         totalSize       : The total size of all downloads once completed.
+   *         totalTransferred: The total amount of transferred data for these
+   *                           downloads.
+   *         slowestSpeed    : The slowest download rate.
+   *         rawTimeLeft     : The estimated time left for the downloads to
+   *                           complete.
+   *         percentComplete : The percentage of bytes successfully downloaded.
+   */
+  summarizeDownloads(downloads) {
+    let summary = {
+      numActive: 0,
+      numPaused: 0,
+      numDownloading: 0,
+      totalSize: 0,
+      totalTransferred: 0,
+      // slowestSpeed is Infinity so that we can use Math.min to
+      // find the slowest speed. We'll set this to 0 afterwards if
+      // it's still at Infinity by the time we're done iterating all
+      // download.
+      slowestSpeed: Infinity,
+      rawTimeLeft: -1,
+      percentComplete: -1
+    }
+
+    for (let download of downloads) {
+      summary.numActive++;
+
+      if (!download.stopped) {
+        summary.numDownloading++;
+        if (download.hasProgress && download.speed > 0) {
+          let sizeLeft = download.totalBytes - download.currentBytes;
+          summary.rawTimeLeft = Math.max(summary.rawTimeLeft,
+                                         sizeLeft / download.speed);
+          summary.slowestSpeed = Math.min(summary.slowestSpeed,
+                                          download.speed);
+        }
+      } else if (download.canceled && download.hasPartialData) {
+        summary.numPaused++;
+      }
+      // Only add to total values if we actually know the download size.
+      if (download.succeeded) {
+        summary.totalSize += download.target.size;
+        summary.totalTransferred += download.target.size;
+      } else if (download.hasProgress) {
+        summary.totalSize += download.totalBytes;
+        summary.totalTransferred += download.currentBytes;
+      }
+    }
+
+    if (summary.totalSize != 0) {
+      summary.percentComplete = (summary.totalTransferred /
+                                 summary.totalSize) * 100;
+    }
+
+    if (summary.slowestSpeed == Infinity) {
+      summary.slowestSpeed = 0;
+    }
+
+    return summary;
+  },
+
+  /**
+   * If necessary, smooths the estimated number of seconds remaining for one
+   * or more downloads to complete.
+   *
+   * @param aSeconds
+   *        Current raw estimate on number of seconds left for one or more
+   *        downloads. This is a floating point value to help get sub-second
+   *        accuracy for current and future estimates.
+   */
+  smoothSeconds: function DC_smoothSeconds(aSeconds, aLastSeconds)
+  {
+    // We apply an algorithm similar to the DownloadUtils.getTimeLeft function,
+    // though tailored to a single time estimation for all downloads.  We never
+    // apply something if the new value is less than half the previous value.
+    let shouldApplySmoothing = aLastSeconds >= 0 &&
+                               aSeconds > aLastSeconds / 2;
+    if (shouldApplySmoothing) {
+      // Apply hysteresis to favor downward over upward swings.  Trust only 30%
+      // of the new value if lower, and 10% if higher (exponential smoothing).
+      let diff = aSeconds - aLastSeconds;
+      aSeconds = aLastSeconds + (diff < 0 ? .3 : .1) * diff;
+      
+      // If the new time is similar, reuse something close to the last time
+      // left, but subtract a little to provide forward progress.
+      diff = aSeconds - aLastSeconds;
+      let diffPercent = diff / aLastSeconds * 100;
+      if (Math.abs(diff) < 5 || Math.abs(diffPercent) < 5) {
+        aSeconds = aLastSeconds - (diff < 0 ? .4 : .2);
+      }
+    }
+
+    // In the last few seconds of downloading, we are always subtracting and
+    // never adding to the time left.  Ensure that we never fall below one
+    // second left until all downloads are actually finished.
+    return aLastSeconds = Math.max(aSeconds, 1);
+  },
+
+  /**
+   * Opens a downloaded file.
+   *
+   * @param aFile
+   *        the downloaded file to be opened.
+   * @param aMimeInfo
+   *        the mime type info object.  May be null.
+   * @param aOwnerWindow
+   *        the window with which this action is associated.
+   */
+  openDownloadedFile: function DC_openDownloadedFile(aFile, aMimeInfo, aOwnerWindow) {
+    if (!(aFile instanceof Ci.nsIFile))
+      throw new Error("aFile must be a nsIFile object");
+    if (aMimeInfo && !(aMimeInfo instanceof Ci.nsIMIMEInfo))
+      throw new Error("Invalid value passed for aMimeInfo");
+    if (!(aOwnerWindow instanceof Ci.nsIDOMWindow))
+      throw new Error("aOwnerWindow must be a dom-window object");
+
+#ifdef XP_WIN
+    // On Windows, the system will provide a native confirmation prompt
+    // for .exe files. Exclude this from our prompt, but prompt on other
+    // executable types.
+    let isWindowsExe = aFile.leafName.toLowerCase().endsWith(".exe");
+#else
+    let isWindowsExe = false;
+#endif
+
+    // Confirm opening executable files if required.
+    if (aFile.isExecutable() && !isWindowsExe) {
+      let showAlert = true;
+      try {
+        showAlert = Services.prefs.getBoolPref(kPrefConfirmOpenExe);
+      } catch (ex) {
+        // If the preference does not exist, continue with the prompt.
+      }
+
+      if (showAlert) {
+        let name = aFile.leafName;
+        let message =
+          DownloadsCommon.strings.fileExecutableSecurityWarning(name, name);
+        let title =
+          DownloadsCommon.strings.fileExecutableSecurityWarningTitle;
+
+        let open = Services.prompt.confirm(aOwnerWindow, title, message);
+        if (!open) {
+          return;
+        }
+      }
+    }
+
+    // Actually open the file.
+    try {
+      if (aMimeInfo && aMimeInfo.preferredAction == aMimeInfo.useHelperApp) {
+        aMimeInfo.launchWithFile(aFile);
+        return;
+      }
+    }
+    catch(ex) { }
+
+    // If either we don't have the mime info, or the preferred action failed,
+    // attempt to launch the file directly.
+    try {
+      aFile.launch();
+    }
+    catch(ex) {
+      // If launch fails, try sending it through the system's external "file:"
+      // URL handler.
+      Cc["@mozilla.org/uriloader/external-protocol-service;1"]
+        .getService(Ci.nsIExternalProtocolService)
+        .loadUrl(NetUtil.newURI(aFile));
+    }
+  },
+
+  /**
+   * Show a downloaded file in the system file manager.
+   *
+   * @param aFile
+   *        a downloaded file.
+   */
+  showDownloadedFile: function DC_showDownloadedFile(aFile) {
+    if (!(aFile instanceof Ci.nsIFile))
+      throw new Error("aFile must be a nsIFile object");
+    try {
+      // Show the directory containing the file and select the file.
+      aFile.reveal();
+    } catch (ex) {
+      // If reveal fails for some reason (e.g., it's not implemented on unix
+      // or the file doesn't exist), try using the parent if we have it.
+      let parent = aFile.parent;
+      if (parent) {
+        try {
+          // Open the parent directory to show where the file should be.
+          parent.launch();
+        } catch (ex) {
+          // If launch also fails (probably because it's not implemented), let
+          // the OS handler try to open the parent.
+          Cc["@mozilla.org/uriloader/external-protocol-service;1"]
+            .getService(Ci.nsIExternalProtocolService)
+            .loadUrl(NetUtil.newURI(parent));
+        }
+      }
+    }
+  }
+};
+
+/**
+ * Returns true if we are executing on Windows Vista or a later version.
+ */
+XPCOMUtils.defineLazyGetter(DownloadsCommon, "isWinVistaOrHigher", function () {
+  let os = Cc["@mozilla.org/xre/app-info;1"].getService(Ci.nsIXULRuntime).OS;
+  if (os != "WINNT") {
+    return false;
+  }
+  let sysInfo = Cc["@mozilla.org/system-info;1"].getService(Ci.nsIPropertyBag2);
+  return parseFloat(sysInfo.getProperty("version")) >= 6;
+});
+
+/**
+ * Returns true to indicate that we should hook the panel to the JavaScript API
+ * for downloads instead of the nsIDownloadManager back-end.
+ * This is kept for compatibility/leftovers and should be removed later.
+ */
+XPCOMUtils.defineLazyGetter(DownloadsCommon, "useJSTransfer", function () {
+  return true;
+});
+
+////////////////////////////////////////////////////////////////////////////////
+//// DownloadsData
+
+/**
+ * Retrieves the list of past and completed downloads from the underlying
+ * Download Manager data, and provides asynchronous notifications allowing to
+ * build a consistent view of the available data.
+ *
+ * This object responds to real-time changes in the underlying Download Manager
+ * data.  For example, the deletion of one or more downloads is notified through
+ * the nsIObserver interface, while any state or progress change is notified
+ * through the nsIDownloadProgressListener interface.
+ *
+ * Note that using this object does not automatically start the Download Manager
+ * service.  Consumers will see an empty list of downloads until the service is
+ * actually started.  This is useful to display a neutral progress indicator in
+ * the main browser window until the autostart timeout elapses.
+ *
+ * Note that DownloadsData and PrivateDownloadsData are two equivalent singleton
+ * objects, one accessing non-private downloads, and the other accessing private
+ * ones.
+ */
+function DownloadsDataCtor(aPrivate) {
+  this._isPrivate = aPrivate;
+
+  // Contains all the available Download objects and their integer state.
+  this.oldDownloadStates = new Map();
+
+  // Array of view objects that should be notified when the available download
+  // data changes.
+  this._views = [];
+}
+
+DownloadsDataCtor.prototype = {
+  /**
+   * Starts receiving events for current downloads.
+   */
+  initializeDataLink() {
+    if (!this._dataLinkInitialized) {
+      let promiseList = Downloads.getList(this._isPrivate ? Downloads.PRIVATE
+                                                          : Downloads.PUBLIC);
+      promiseList.then(list => list.addView(this)).then(null, Cu.reportError);
+      this._dataLinkInitialized = true;
+    }
+  },
+  _dataLinkInitialized: false,
+
+  /**
+   * Stops receiving events for current downloads and cancels any pending read.
+   */
+  terminateDataLink: function DD_terminateDataLink()
+  {
+    Cu.reportError("terminateDataLink not applicable with JS Transfers");
+    return;
+  },
+
+  /**
+   * Iterator for all the available Download objects. This is empty until the
+   * data has been loaded using the JavaScript API for downloads.
+   */
+  get downloads() this.oldDownloadStates.keys(),
+
+  /**
+   * True if there are finished downloads that can be removed from the list.
+   */
+  get canRemoveFinished()
+  {
+    for (let download of this.downloads) {
+      // Stopped, paused, and failed downloads with partial data are removed.
+      if (download.stopped && !(download.canceled && download.hasPartialData)) {
+        return true;
+      }
+    }
+    return false;
+  },
+
+  /**
+   * Asks the back-end to remove finished downloads from the list.
+   */
+  removeFinished: function DD_removeFinished()
+  {
+    let promiseList = Downloads.getList(this._isPrivate ? Downloads.PRIVATE
+                                                        : Downloads.PUBLIC);
+    promiseList.then(list => list.removeFinished())
+               .then(null, Cu.reportError);
+  },
+
+  //////////////////////////////////////////////////////////////////////////////
+  //// Integration with the asynchronous Downloads back-end
+
+  onDownloadAdded(download) {
+    // Download objects do not store the end time of downloads, as the Downloads
+    // API does not need to persist this information for all platforms. Once a
+    // download terminates on a Desktop browser, it becomes a history download,
+    // for which the end time is stored differently, as a Places annotation.
+    download.endTime = Date.now();
+
+    this.oldDownloadStates.set(download,
+                               DownloadsCommon.stateOfDownload(download));
+
+    for (let view of this._views) {
+      view.onDownloadAdded(download, true);
+    }
+  },
+
+  onDownloadChanged(download) {
+    let oldState = this.oldDownloadStates.get(download);
+    let newState = DownloadsCommon.stateOfDownload(download);
+    this.oldDownloadStates.set(download, newState);
+
+    if (oldState != newState) {
+      if (download.succeeded ||
+          (download.canceled && !download.hasPartialData) ||
+          download.error) {
+        // Store the end time that may be displayed by the views.
+        download.endTime = Date.now();
+
+        // This state transition code should actually be located in a Downloads
+        // API module (bug 941009).  Moreover, the fact that state is stored as
+        // annotations should be ideally hidden behind methods of
+        // nsIDownloadHistory (bug 830415).
+        if (!this._isPrivate) {
+          try {
+            let downloadMetaData = {
+              state: DownloadsCommon.stateOfDownload(download),
+              endTime: download.endTime,
+            };
+            if (download.succeeded) {
+              downloadMetaData.fileSize = download.target.size;
+            }
+  
+            PlacesUtils.annotations.setPageAnnotation(
+                          NetUtil.newURI(download.source.url),
+                          "downloads/metaData",
+                          JSON.stringify(downloadMetaData), 0,
+                          PlacesUtils.annotations.EXPIRE_WITH_HISTORY);
+          } catch (ex) {
+            Cu.reportError(ex);
+          }
+        }
+      }
+
+      for (let view of this._views) {
+        try {
+          view.onDownloadStateChanged(download);
+        } catch (ex) {
+          Cu.reportError(ex);
+        }
+      }
+
+      if (download.succeeded ||
+          (download.error && download.error.becauseBlocked)) {
+        this._notifyDownloadEvent("finish");
+      }
+    }
+
+    if (!download.newDownloadNotified) {
+      download.newDownloadNotified = true;
+      this._notifyDownloadEvent("start");
+    }
+
+    for (let view of this._views) {
+      view.onDownloadChanged(download);
+    }
+  },
+
+  onDownloadRemoved(download) {
+    this.oldDownloadStates.delete(download);
+
+    for (let view of this._views) {
+      view.onDownloadRemoved(download);
+    }
+  },
+
+  //////////////////////////////////////////////////////////////////////////////
+  //// Registration of views
+
+  /**
+   * Adds an object to be notified when the available download data changes.
+   * The specified object is initialized with the currently available downloads.
+   *
+   * @param aView
+   *        DownloadsView object to be added.  This reference must be passed to
+   *        removeView before termination.
+   */
+  addView: function DD_addView(aView)
+  {
+    this._views.push(aView);
+    this._updateView(aView);
+  },
+
+  /**
+   * Removes an object previously added using addView.
+   *
+   * @param aView
+   *        DownloadsView object to be removed.
+   */
+  removeView: function DD_removeView(aView)
+  {
+    let index = this._views.indexOf(aView);
+    if (index != -1) {
+      this._views.splice(index, 1);
+    }
+  },
+
+  /**
+   * Ensures that the currently loaded data is added to the specified view.
+   *
+   * @param aView
+   *        DownloadsView object to be initialized.
+   */
+  _updateView: function DD_updateView(aView)
+  {
+    // Indicate to the view that a batch loading operation is in progress.
+    aView.onDataLoadStarting();
+
+    // Sort backwards by start time, ensuring that the most recent
+    // downloads are added first regardless of their state.
+    // Tycho:
+    //let loadedItemsArray = [dataItem
+    //                        for each (dataItem in this.dataItems)
+    //                        if (dataItem)];
+    let downloadsArray = [...this.downloads];
+    downloadsArray.sort((a, b) => b.startTime - a.startTime);
+    downloadsArray.forEach(download => aView.onDownloadAdded(download, false));
+
+    // Notify the view that all data is available unless loading is in progress.
+    if (!this._pendingStatement) {
+      aView.onDataLoadCompleted();
+    }
+  },
+
+  //////////////////////////////////////////////////////////////////////////////
+  //// In-memory downloads data store
+
+  /**
+   * Clears the loaded data.
+   */
+  clear: function DD_clear()
+  {
+    this._terminateDataAccess();
+    this.dataItems = {};
+  },
+
+  /**
+   * Returns the data item associated with the provided source object.  The
+   * source can be a download object that we received from the Download Manager
+   * because of a real-time notification, or a row from the downloads database,
+   * during the asynchronous data load.
+   *
+   * In case we receive download status notifications while we are still
+   * populating the list of downloads from the database, we want the real-time
+   * status to take precedence over the state that is read from the database,
+   * which might be older.  This is achieved by creating the download item if
+   * it's not already in the list, but never updating the returned object using
+   * the data from the database, if the object already exists.
+   *
+   * @param aSource
+   *        Object containing the data with which the item should be initialized
+   *        if it doesn't already exist in the list.  This should implement
+   *        either nsIDownload or mozIStorageRow.  If the item exists, this
+   *        argument is only used to retrieve the download identifier.
+   * @param aMayReuseGUID
+   *        If false, indicates that the download should not be added if a
+   *        download with the same identifier was removed in the meantime.  This
+   *        ensures that, while loading the list asynchronously, downloads that
+   *        have been removed in the meantime do no reappear inadvertently.
+   *
+   * @return New or existing data item, or null if the item was deleted from the
+   *         list of available downloads.
+   */
+  _getOrAddDataItem: function DD_getOrAddDataItem(aSource, aMayReuseGUID)
+  {
+    let downloadGuid = (aSource instanceof Ci.nsIDownload)
+                       ? aSource.guid
+                       : aSource.getResultByName("guid");
+    if (downloadGuid in this.dataItems) {
+      let existingItem = this.dataItems[downloadGuid];
+      if (existingItem || !aMayReuseGUID) {
+        // Returns null if the download was removed and we can't reuse the item.
+        return existingItem;
+      }
+    }
+    DownloadsCommon.log("Creating a new DownloadsDataItem with downloadGuid =",
+                        downloadGuid);
+    let dataItem = new DownloadsDataItem(aSource);
+    this.dataItems[downloadGuid] = dataItem;
+
+    // Create the view items before returning.
+    let addToStartOfList = aSource instanceof Ci.nsIDownload;
+    this._views.forEach(
+      function (view) view.onDataItemAdded(dataItem, addToStartOfList)
+    );
+    return dataItem;
+  },
+
+  /**
+   * Removes the data item with the specified identifier.
+   *
+   * This method can be called at most once per download identifier.
+   */
+  _removeDataItem: function DD_removeDataItem(aDownloadId)
+  {
+    if (aDownloadId in this.dataItems) {
+      let dataItem = this.dataItems[aDownloadId];
+      this.dataItems[aDownloadId] = null;
+      this._views.forEach(
+        function (view) view.onDataItemRemoved(dataItem)
+      );
+    }
+  },
+
+  //////////////////////////////////////////////////////////////////////////////
+  //// Persistent data loading
+
+  /**
+   * Represents an executing statement, allowing its cancellation.
+   */
+  _pendingStatement: null,
+
+  /**
+   * Indicates which kind of items from the persistent downloads database have
+   * been fully loaded in memory and are available to the views.  This can
+   * assume the value of one of the kLoad constants.
+   */
+  _loadState: 0,
+
+  /** No downloads have been fully loaded yet. */
+  get kLoadNone() 0,
+  /** All the active downloads in the database are loaded in memory. */
+  get kLoadActive() 1,
+  /** All the downloads in the database are loaded in memory. */
+  get kLoadAll() 2,
+
+  /**
+   * Reloads the specified kind of downloads from the persistent database.  This
+   * method must only be called when Private Browsing Mode is disabled.
+   *
+   * @param aActiveOnly
+   *        True to load only active downloads from the database.
+   */
+  ensurePersistentDataLoaded:
+  function DD_ensurePersistentDataLoaded(aActiveOnly)
+  {
+    if (this == PrivateDownloadsData) {
+      Cu.reportError("ensurePersistentDataLoaded should not be called on PrivateDownloadsData");
+      return;
+    }
+
+    if (this._pendingStatement) {
+      // We are already in the process of reloading all downloads.
+      return;
+    }
+
+    if (aActiveOnly) {
+      if (this._loadState == this.kLoadNone) {
+        DownloadsCommon.log("Loading only active downloads from the persistence database");
+        // Indicate to the views that a batch loading operation is in progress.
+        this._views.forEach(
+          function (view) view.onDataLoadStarting()
+        );
+
+        // Reload the list using the Download Manager service.  The list is
+        // returned in no particular order.
+        let downloads = Services.downloads.activeDownloads;
+        while (downloads.hasMoreElements()) {
+          let download = downloads.getNext().QueryInterface(Ci.nsIDownload);
+          this._getOrAddDataItem(download, true);
+        }
+        this._loadState = this.kLoadActive;
+
+        // Indicate to the views that the batch loading operation is complete.
+        this._views.forEach(
+          function (view) view.onDataLoadCompleted()
+        );
+        DownloadsCommon.log("Active downloads done loading.");
+      }
+    } else {
+      if (this._loadState != this.kLoadAll) {
+        // Load only the relevant columns from the downloads database.  The
+        // columns are read in the _initFromDataRow method of DownloadsDataItem.
+        // Order by descending download identifier so that the most recent
+        // downloads are notified first to the listening views.
+        DownloadsCommon.log("Loading all downloads from the persistence database.");
+        let dbConnection = Services.downloads.DBConnection;
+        let statement = dbConnection.createAsyncStatement(
+          "SELECT guid, target, name, source, referrer, state, "
+        +        "startTime, endTime, currBytes, maxBytes "
+        + "FROM moz_downloads "
+        + "ORDER BY startTime DESC"
+        );
+        try {
+          this._pendingStatement = statement.executeAsync(this);
+        } finally {
+          statement.finalize();
+        }
+      }
+    }
+  },
+
+  /**
+   * Cancels any pending data access and ensures views are notified.
+   */
+  _terminateDataAccess: function DD_terminateDataAccess()
+  {
+    if (this._pendingStatement) {
+      this._pendingStatement.cancel();
+      this._pendingStatement = null;
+    }
+
+    // Close all the views on the current data.  Create a copy of the array
+    // because some views might unregister while processing this event.
+    Array.slice(this._views, 0).forEach(
+      function (view) view.onDataInvalidated()
+    );
+  },
+
+  //////////////////////////////////////////////////////////////////////////////
+  //// mozIStorageStatementCallback
+
+  handleResult: function DD_handleResult(aResultSet)
+  {
+    for (let row = aResultSet.getNextRow();
+         row;
+         row = aResultSet.getNextRow()) {
+      // Add the download to the list and initialize it with the data we read,
+      // unless we already received a notification providing more reliable
+      // information for this download.
+      this._getOrAddDataItem(row, false);
+    }
+  },
+
+  handleError: function DD_handleError(aError)
+  {
+    DownloadsCommon.error("Database statement execution error (",
+                          aError.result, "): ", aError.message);
+  },
+
+  handleCompletion: function DD_handleCompletion(aReason)
+  {
+    DownloadsCommon.log("Loading all downloads from database completed with reason:",
+                        aReason);
+    this._pendingStatement = null;
+
+    // To ensure that we don't inadvertently delete more downloads from the
+    // database than needed on shutdown, we should update the load state only if
+    // the operation completed successfully.
+    if (aReason == Ci.mozIStorageStatementCallback.REASON_FINISHED) {
+      this._loadState = this.kLoadAll;
+    }
+
+    // Indicate to the views that the batch loading operation is complete, even
+    // if the lookup failed or was canceled.  The only possible glitch happens
+    // in case the database backend changes while loading data, when the views
+    // would open and immediately close.  This case is rare enough not to need a
+    // special treatment.
+    this._views.forEach(
+      function (view) view.onDataLoadCompleted()
+    );
+  },
+
+  //////////////////////////////////////////////////////////////////////////////
+  //// nsIObserver
+
+  observe: function DD_observe(aSubject, aTopic, aData)
+  {
+    switch (aTopic) {
+      case "download-manager-remove-download-guid":
+        // If a single download was removed, remove the corresponding data item.
+        if (aSubject) {
+            let downloadGuid = aSubject.QueryInterface(Ci.nsISupportsCString).data;
+            DownloadsCommon.log("A single download with id",
+                                downloadGuid, "was removed.");
+          this._removeDataItem(downloadGuid);
+          break;
+        }
+
+        // Multiple downloads have been removed.  Iterate over known downloads
+        // and remove those that don't exist anymore.
+        DownloadsCommon.log("Multiple downloads were removed.");
+        for each (let dataItem in this.dataItems) {
+          if (dataItem) {
+            // Bug 449811 - We have to bind to the dataItem because Javascript
+            // doesn't do fresh let-bindings per loop iteration.
+            let dataItemBinding = dataItem;
+            Services.downloads.getDownloadByGUID(dataItemBinding.downloadGuid,
+                                                 function(aStatus, aResult) {
+              if (aStatus == Components.results.NS_ERROR_NOT_AVAILABLE) {
+                DownloadsCommon.log("Removing download with id",
+                                    dataItemBinding.downloadGuid);
+                this._removeDataItem(dataItemBinding.downloadGuid);
+              }
+            }.bind(this));
+          }
+        }
+        break;
+    }
+  },
+
+  //////////////////////////////////////////////////////////////////////////////
+  //// nsIDownloadProgressListener
+
+  onDownloadStateChange: function DD_onDownloadStateChange(aOldState, aDownload)
+  {
+    if (aDownload.isPrivate != this._isPrivate) {
+      // Ignore the downloads with a privacy status other than what we are
+      // tracking.
+      return;
+    }
+
+    // When a new download is added, it may have the same identifier of a
+    // download that we previously deleted during this session, and we also
+    // want to provide a visible indication that the download started.
+    let isNew = aOldState == nsIDM.DOWNLOAD_NOTSTARTED ||
+                aOldState == nsIDM.DOWNLOAD_QUEUED;
+
+    let dataItem = this._getOrAddDataItem(aDownload, isNew);
+    if (!dataItem) {
+      return;
+    }
+
+    let wasInProgress = dataItem.inProgress;
+
+    DownloadsCommon.log("A download changed its state to:", aDownload.state);
+    dataItem.state = aDownload.state;
+    dataItem.referrer = aDownload.referrer && aDownload.referrer.spec;
+    dataItem.resumable = aDownload.resumable;
+    dataItem.startTime = Math.round(aDownload.startTime / 1000);
+    dataItem.currBytes = aDownload.amountTransferred;
+    dataItem.maxBytes = aDownload.size;
+
+    if (wasInProgress && !dataItem.inProgress) {
+      dataItem.endTime = Date.now();
+    }
+
+    // When a download is retried, we create a different download object from
+    // the database with the same ID as before. This means that the nsIDownload
+    // that the dataItem holds might now need updating.
+    //
+    // We only overwrite this in the event that _download exists, because if it
+    // doesn't, that means that no caller ever tried to get the nsIDownload,
+    // which means it was never retrieved and doesn't need to be overwritten.
+    if (dataItem._download) {
+      dataItem._download = aDownload;
+    }
+
+    for (let view of this._views) {
+      try {
+        view.getViewItem(dataItem).onStateChange(aOldState);
+      } catch (ex) {
+        Cu.reportError(ex);
+      }
+    }
+
+    if (isNew && !dataItem.newDownloadNotified) {
+      dataItem.newDownloadNotified = true;
+      this._notifyDownloadEvent("start");
+    }
+
+    // This is a final state of which we are only notified once.
+    if (dataItem.done) {
+      this._notifyDownloadEvent("finish");
+    }
+
+    // TODO Bug 830415: this isn't the right place to set these annotation.
+    // It should be set it in places' nsIDownloadHistory implementation.
+    if (!this._isPrivate && !dataItem.inProgress) {
+      let downloadMetaData = { state: dataItem.state,
+                               endTime: dataItem.endTime };
+      if (dataItem.done)
+        downloadMetaData.fileSize = dataItem.maxBytes;
+
+      try {
+        PlacesUtils.annotations.setPageAnnotation(
+          NetUtil.newURI(dataItem.uri), "downloads/metaData", JSON.stringify(downloadMetaData), 0,
+          PlacesUtils.annotations.EXPIRE_WITH_HISTORY);
+      }
+      catch(ex) {
+        Cu.reportError(ex);
+      }
+    }
+  },
+
+  onProgressChange: function DD_onProgressChange(aWebProgress, aRequest,
+                                                  aCurSelfProgress,
+                                                  aMaxSelfProgress,
+                                                  aCurTotalProgress,
+                                                  aMaxTotalProgress, aDownload)
+  {
+    if (aDownload.isPrivate != this._isPrivate) {
+      // Ignore the downloads with a privacy status other than what we are
+      // tracking.
+      return;
+    }
+
+    let dataItem = this._getOrAddDataItem(aDownload, false);
+    if (!dataItem) {
+      return;
+    }
+
+    dataItem.currBytes = aDownload.amountTransferred;
+    dataItem.maxBytes = aDownload.size;
+    dataItem.speed = aDownload.speed;
+    dataItem.percentComplete = aDownload.percentComplete;
+
+    this._views.forEach(
+      function (view) view.getViewItem(dataItem).onProgressChange()
+    );
+  },
+
+  onStateChange: function () { },
+
+  onSecurityChange: function () { },
+
+  //////////////////////////////////////////////////////////////////////////////
+  //// Notifications sent to the most recent browser window only
+
+  /**
+   * Set to true after the first download causes the downloads panel to be
+   * displayed.
+   */
+  get panelHasShownBefore() {
+    try {
+      return Services.prefs.getBoolPref("browser.download.panel.shown");
+    } catch (ex) { }
+    return false;
+  },
+
+  set panelHasShownBefore(aValue) {
+    Services.prefs.setBoolPref("browser.download.panel.shown", aValue);
+    return aValue;
+  },
+
+  /**
+   * Displays a new or finished download notification in the most recent browser
+   * window, if one is currently available with the required privacy type.
+   *
+   * @param aType
+   *        Set to "start" for new downloads, "finish" for completed downloads.
+   */
+  _notifyDownloadEvent: function DD_notifyDownloadEvent(aType)
+  {
+    DownloadsCommon.log("Attempting to notify that a new download has started or finished.");
+    if (DownloadsCommon.useToolkitUI) {
+      DownloadsCommon.log("Cancelling notification - we're using the toolkit downloads manager.");
+      return;
+    }
+
+    // Show the panel in the most recent browser window, if present.
+    let browserWin = RecentWindow.getMostRecentBrowserWindow({ private: this._isPrivate });
+    if (!browserWin) {
+      return;
+    }
+
+    if (this.panelHasShownBefore) {
+      // For new downloads after the first one, don't show the panel
+      // automatically, but provide a visible notification in the topmost
+      // browser window, if the status indicator is already visible.
+      DownloadsCommon.log("Showing new download notification.");
+      browserWin.DownloadsIndicatorView.showEventNotification(aType);
+      return;
+    }
+    this.panelHasShownBefore = true;
+    browserWin.DownloadsPanel.showPanel();
+  }
+};
+
+XPCOMUtils.defineLazyGetter(this, "PrivateDownloadsData", function() {
+  return new DownloadsDataCtor(true);
+});
+
+XPCOMUtils.defineLazyGetter(this, "DownloadsData", function() {
+  return new DownloadsDataCtor(false);
+});
+
+////////////////////////////////////////////////////////////////////////////////
+//// DownloadsViewPrototype
+
+/**
+ * A prototype for an object that registers itself with DownloadsData as soon
+ * as a view is registered with it.
+ */
+const DownloadsViewPrototype = {
+  //////////////////////////////////////////////////////////////////////////////
+  //// Registration of views
+
+  /**
+   * Array of view objects that should be notified when the available status
+   * data changes.
+   *
+   * SUBCLASSES MUST OVERRIDE THIS PROPERTY.
+   */
+  _views: null,
+
+  /**
+   * Determines whether this view object is over the private or non-private
+   * downloads.
+   *
+   * SUBCLASSES MUST OVERRIDE THIS PROPERTY.
+   */
+  _isPrivate: false,
+
+  /**
+   * Adds an object to be notified when the available status data changes.
+   * The specified object is initialized with the currently available status.
+   *
+   * @param aView
+   *        View object to be added.  This reference must be
+   *        passed to removeView before termination.
+   */
+  addView: function DVP_addView(aView)
+  {
+    // Start receiving events when the first of our views is registered.
+    if (this._views.length == 0) {
+      if (this._isPrivate) {
+        PrivateDownloadsData.addView(this);
+      } else {
+        DownloadsData.addView(this);
+      }
+    }
+
+    this._views.push(aView);
+    this.refreshView(aView);
+  },
+
+  /**
+   * Updates the properties of an object previously added using addView.
+   *
+   * @param aView
+   *        View object to be updated.
+   */
+  refreshView: function DVP_refreshView(aView)
+  {
+    // Update immediately even if we are still loading data asynchronously.
+    // Subclasses must provide these two functions!
+    this._refreshProperties();
+    this._updateView(aView);
+  },
+
+  /**
+   * Removes an object previously added using addView.
+   *
+   * @param aView
+   *        View object to be removed.
+   */
+  removeView: function DVP_removeView(aView)
+  {
+    let index = this._views.indexOf(aView);
+    if (index != -1) {
+      this._views.splice(index, 1);
+    }
+
+    // Stop receiving events when the last of our views is unregistered.
+    if (this._views.length == 0) {
+      if (this._isPrivate) {
+        PrivateDownloadsData.removeView(this);
+      } else {
+        DownloadsData.removeView(this);
+      }
+    }
+  },
+
+  //////////////////////////////////////////////////////////////////////////////
+  //// Callback functions from DownloadsData
+
+  /**
+   * Indicates whether we are still loading downloads data asynchronously.
+   */
+  _loading: false,
+
+  /**
+   * Called before multiple downloads are about to be loaded.
+   */
+  onDataLoadStarting: function DVP_onDataLoadStarting()
+  {
+    this._loading = true;
+  },
+
+  /**
+   * Called after data loading finished.
+   */
+  onDataLoadCompleted: function DVP_onDataLoadCompleted()
+  {
+    this._loading = false;
+  },
+
+  /**
+   * Called when the downloads database becomes unavailable (for example, we
+   * entered Private Browsing Mode and the database backend changed).
+   * References to existing data should be discarded.
+   *
+   * @note Subclasses should override this.
+   */
+  onDataInvalidated: function DVP_onDataInvalidated()
+  {
+    throw Components.results.NS_ERROR_NOT_IMPLEMENTED;
+  },
+
+  /**
+   * Called when a new download data item is available, either during the
+   * asynchronous data load or when a new download is started.
+   *
+   * @param download
+   *        Download object that was just added.
+   * @param newest
+   *        When true, indicates that this item is the most recent and should be
+   *        added in the topmost position.  This happens when a new download is
+   *        started.  When false, indicates that the item is the least recent
+   *        with regard to the items that have been already added. The latter
+   *        generally happens during the asynchronous data load.
+   *
+   * @note Subclasses should override this.
+   */
+  onDownloadAdded(download, newest) {
+    throw Components.results.NS_ERROR_NOT_IMPLEMENTED;
+  },
+
+  /**
+   * Called when the overall state of a Download has changed. In particular,
+   * this is called only once when the download succeeds or is blocked
+   * permanently, and is never called if only the current progress changed.
+   *
+   * The onDownloadChanged notification will always be sent afterwards.
+   *
+   * @note Subclasses should override this.
+   */
+  onDownloadStateChanged(download) {
+    throw Components.results.NS_ERROR_NOT_IMPLEMENTED;
+  },
+
+  /**
+   * Called every time any state property of a Download may have changed,
+   * including progress properties.
+   *
+   * Note that progress notification changes are throttled at the Downloads.jsm
+   * API level, and there is no throttling mechanism in the front-end.
+   *
+   * @note Subclasses should override this.
+   */
+  onDownloadChanged(download) {
+    throw Components.results.NS_ERROR_NOT_IMPLEMENTED;
+  },
+
+  /**
+   * Called when a data item is removed, ensures that the widget associated with
+   * the view item is removed from the user interface.
+   *
+   * @param download
+   *        Download object that is being removed.
+   *
+   * @note Subclasses should override this.
+   */
+  onDownloadRemoved(download) {
+    throw Components.results.NS_ERROR_NOT_IMPLEMENTED;
+  },
+
+  /**
+   * Private function used to refresh the internal properties being sent to
+   * each registered view.
+   *
+   * @note Subclasses should override this.
+   */
+  _refreshProperties: function DID_refreshProperties()
+  {
+    throw Components.results.NS_ERROR_NOT_IMPLEMENTED;
+  },
+
+  /**
+   * Private function used to refresh an individual view.
+   *
+   * @note Subclasses should override this.
+   */
+  _updateView: function DID_updateView()
+  {
+    throw Components.results.NS_ERROR_NOT_IMPLEMENTED;
+  }
+};
+
+////////////////////////////////////////////////////////////////////////////////
+//// DownloadsIndicatorData
+
+/**
+ * This object registers itself with DownloadsData as a view, and transforms the
+ * notifications it receives into overall status data, that is then broadcast to
+ * the registered download status indicators.
+ *
+ * Note that using this object does not automatically start the Download Manager
+ * service.  Consumers will see an empty list of downloads until the service is
+ * actually started.  This is useful to display a neutral progress indicator in
+ * the main browser window until the autostart timeout elapses.
+ */
+function DownloadsIndicatorDataCtor(aPrivate) {
+  this._isPrivate = aPrivate;
+  this._views = [];
+}
+DownloadsIndicatorDataCtor.prototype = {
+  __proto__: DownloadsViewPrototype,
+
+  /**
+   * Removes an object previously added using addView.
+   *
+   * @param aView
+   *        DownloadsIndicatorView object to be removed.
+   */
+  removeView: function DID_removeView(aView)
+  {
+    DownloadsViewPrototype.removeView.call(this, aView);
+
+    if (this._views.length == 0) {
+      this._itemCount = 0;
+    }
+  },
+
+  //////////////////////////////////////////////////////////////////////////////
+  //// Callback functions from DownloadsData
+
+  onDataLoadCompleted: function DID_onDataLoadCompleted()
+  {
+    DownloadsViewPrototype.onDataLoadCompleted.call(this);
+    this._updateViews();
+  },
+
+  /**
+   * Called when the downloads database becomes unavailable (for example, we
+   * entered Private Browsing Mode and the database backend changed).
+   * References to existing data should be discarded.
+   */
+  onDataInvalidated: function DID_onDataInvalidated()
+  {
+    this._itemCount = 0;
+  },
+
+  onDownloadAdded(download, newest) {
+    this._itemCount++;
+    this._updateViews();
+  },
+
+  onDownloadStateChanged(download) {
+    if (download.succeeded || download.error) {
+      this.attention = true;
+    }
+
+    // Since the state of a download changed, reset the estimated time left.
+    this._lastRawTimeLeft = -1;
+    this._lastTimeLeft = -1;
+  },
+
+  onDownloadChanged(download) {
+    this._updateViews();
+  },
+
+  onDownloadRemoved(download) {
+    this._itemCount--;
+    this._updateViews();
+  },
+
+  //////////////////////////////////////////////////////////////////////////////
+  //// Propagation of properties to our views
+
+  // The following properties are updated by _refreshProperties and are then
+  // propagated to the views.  See _refreshProperties for details.
+  _hasDownloads: false,
+  _counter: "",
+  _percentComplete: -1,
+  _paused: false,
+
+  /**
+   * Indicates whether the download indicators should be highlighted.
+   */
+  set attention(aValue)
+  {
+    this._attention = aValue;
+    this._updateViews();
+    return aValue;
+  },
+  _attention: false,
+
+  /**
+   * Indicates whether the user is interacting with downloads, thus the
+   * attention indication should not be shown even if requested.
+   */
+  set attentionSuppressed(aValue)
+  {
+    this._attentionSuppressed = aValue;
+    this._attention = false;
+    this._updateViews();
+    return aValue;
+  },
+  _attentionSuppressed: false,
+
+  /**
+   * Computes aggregate values and propagates the changes to our views.
+   */
+  _updateViews: function DID_updateViews()
+  {
+    // Do not update the status indicators during batch loads of download items.
+    if (this._loading) {
+      return;
+    }
+
+    this._refreshProperties();
+    this._views.forEach(this._updateView, this);
+  },
+
+  /**
+   * Updates the specified view with the current aggregate values.
+   *
+   * @param aView
+   *        DownloadsIndicatorView object to be updated.
+   */
+  _updateView: function DID_updateView(aView)
+  {
+    aView.hasDownloads = this._hasDownloads;
+    aView.counter = this._counter;
+    aView.percentComplete = this._percentComplete;
+    aView.paused = this._paused;
+    aView.attention = this._attention && !this._attentionSuppressed;
+  },
+
+  //////////////////////////////////////////////////////////////////////////////
+  //// Property updating based on current download status
+
+  /**
+   * Number of download items that are available to be displayed.
+   */
+  _itemCount: 0,
+
+  /**
+   * Floating point value indicating the last number of seconds estimated until
+   * the longest download will finish.  We need to store this value so that we
+   * don't continuously apply smoothing if the actual download state has not
+   * changed.  This is set to -1 if the previous value is unknown.
+   */
+  _lastRawTimeLeft: -1,
+
+  /**
+   * Last number of seconds estimated until all in-progress downloads with a
+   * known size and speed will finish.  This value is stored to allow smoothing
+   * in case of small variations.  This is set to -1 if the previous value is
+   * unknown.
+   */
+  _lastTimeLeft: -1,
+
+  /**
+   * A generator function for the Download objects this summary is currently
+   * interested in. This generator is passed off to summarizeDownloads in order
+   * to generate statistics about the downloads we care about - in this case,
+   * it's all active downloads.
+   */
+  * _activeDownloads() {
+    let downloads = this._isPrivate ? PrivateDownloadsData.downloads
+                                    : DownloadsData.downloads;
+    for (let download of downloads) {
+      if (!download.stopped || (download.canceled && download.hasPartialData)) {
+        yield download;
+      }
+    }
+  },
+
+  /**
+   * Computes aggregate values based on the current state of downloads.
+   */
+  _refreshProperties: function DID_refreshProperties()
+  {
+    let summary =
+      DownloadsCommon.summarizeDownloads(this._activeDownloads());
+
+    // Determine if the indicator should be shown or get attention.
+    this._hasDownloads = (this._itemCount > 0);
+
+    // If all downloads are paused, show the progress indicator as paused.
+    this._paused = summary.numActive > 0 &&
+                   summary.numActive == summary.numPaused;
+
+    this._percentComplete = summary.percentComplete;
+
+    // Display the estimated time left, if present.
+    if (summary.rawTimeLeft == -1) {
+      // There are no downloads with a known time left.
+      this._lastRawTimeLeft = -1;
+      this._lastTimeLeft = -1;
+      this._counter = "";
+    } else {
+      // Compute the new time left only if state actually changed.
+      if (this._lastRawTimeLeft != summary.rawTimeLeft) {
+        this._lastRawTimeLeft = summary.rawTimeLeft;
+        this._lastTimeLeft = DownloadsCommon.smoothSeconds(summary.rawTimeLeft,
+                                                           this._lastTimeLeft);
+      }
+      this._counter = DownloadsCommon.formatTimeLeft(this._lastTimeLeft);
+    }
+  }
+};
+
+XPCOMUtils.defineLazyGetter(this, "PrivateDownloadsIndicatorData", function() {
+  return new DownloadsIndicatorDataCtor(true);
+});
+
+XPCOMUtils.defineLazyGetter(this, "DownloadsIndicatorData", function() {
+  return new DownloadsIndicatorDataCtor(false);
+});
+
+////////////////////////////////////////////////////////////////////////////////
+//// DownloadsSummaryData
+
+/**
+ * DownloadsSummaryData is a view for DownloadsData that produces a summary
+ * of all downloads after a certain exclusion point aNumToExclude. For example,
+ * if there were 5 downloads in progress, and a DownloadsSummaryData was
+ * constructed with aNumToExclude equal to 3, then that DownloadsSummaryData
+ * would produce a summary of the last 2 downloads.
+ *
+ * @param aIsPrivate
+ *        True if the browser window which owns the download button is a private
+ *        window.
+ * @param aNumToExclude
+ *        The number of items to exclude from the summary, starting from the
+ *        top of the list.
+ */
+function DownloadsSummaryData(aIsPrivate, aNumToExclude) {
+  this._numToExclude = aNumToExclude;
+  // Since we can have multiple instances of DownloadsSummaryData, we
+  // override these values from the prototype so that each instance can be
+  // completely separated from one another.
+  this._loading = false;
+
+  this._downloads = [];
+
+  // Floating point value indicating the last number of seconds estimated until
+  // the longest download will finish.  We need to store this value so that we
+  // don't continuously apply smoothing if the actual download state has not
+  // changed.  This is set to -1 if the previous value is unknown.
+  this._lastRawTimeLeft = -1;
+
+  // Last number of seconds estimated until all in-progress downloads with a
+  // known size and speed will finish.  This value is stored to allow smoothing
+  // in case of small variations.  This is set to -1 if the previous value is
+  // unknown.
+  this._lastTimeLeft = -1;
+
+  // The following properties are updated by _refreshProperties and are then
+  // propagated to the views.
+  this._showingProgress = false;
+  this._details = "";
+  this._description = "";
+  this._numActive = 0;
+  this._percentComplete = -1;
+
+  this._isPrivate = aIsPrivate;
+  this._views = [];
+}
+
+DownloadsSummaryData.prototype = {
+  __proto__: DownloadsViewPrototype,
+
+  /**
+   * Removes an object previously added using addView.
+   *
+   * @param aView
+   *        DownloadsSummary view to be removed.
+   */
+  removeView: function DSD_removeView(aView)
+  {
+    DownloadsViewPrototype.removeView.call(this, aView);
+
+    if (this._views.length == 0) {
+      // Clear out our collection of Download objects. If we ever have
+      // another view registered with us, this will get re-populated.
+      this._downloads = [];
+    }
+  },
+
+  //////////////////////////////////////////////////////////////////////////////
+  //// Callback functions from DownloadsData - see the documentation in
+  //// DownloadsViewPrototype for more information on what these functions
+  //// are used for.
+
+  onDataLoadCompleted: function DSD_onDataLoadCompleted()
+  {
+    DownloadsViewPrototype.onDataLoadCompleted.call(this);
+    this._updateViews();
+  },
+
+  onDataInvalidated: function DSD_onDataInvalidated()
+  {
+    this._dataItems = [];
+  },
+
+  onDownloadAdded(download, newest) {
+    if (newest) {
+      this._downloads.unshift(download);
+    } else {
+      this._downloads.push(download);
+    }
+
+    this._updateViews();
+  },
+
+  onDownloadStateChanged() {
+    // Since the state of a download changed, reset the estimated time left.
+    this._lastRawTimeLeft = -1;
+    this._lastTimeLeft = -1;
+  },
+
+  onDownloadChanged() {
+    this._updateViews();
+  },
+
+  onDownloadRemoved(download) {
+    let itemIndex = this._downloads.indexOf(download);
+    this._downloads.splice(itemIndex, 1);
+    this._updateViews();
+  },
+
+  //////////////////////////////////////////////////////////////////////////////
+  //// Propagation of properties to our views
+
+  /**
+   * Computes aggregate values and propagates the changes to our views.
+   */
+  _updateViews: function DSD_updateViews()
+  {
+    // Do not update the status indicators during batch loads of download items.
+    if (this._loading) {
+      return;
+    }
+
+    this._refreshProperties();
+    this._views.forEach(this._updateView, this);
+  },
+
+  /**
+   * Updates the specified view with the current aggregate values.
+   *
+   * @param aView
+   *        DownloadsIndicatorView object to be updated.
+   */
+  _updateView: function DSD_updateView(aView)
+  {
+    aView.showingProgress = this._showingProgress;
+    aView.percentComplete = this._percentComplete;
+    aView.description = this._description;
+    aView.details = this._details;
+  },
+
+  //////////////////////////////////////////////////////////////////////////////
+  //// Property updating based on current download status
+
+  /**
+   * A generator function for the Download objects this summary is currently
+   * interested in. This generator is passed off to summarizeDownloads in order
+   * to generate statistics about the downloads we care about - in this case,
+   * it's the downloads in this._downloads after the first few to exclude,
+   * which was set when constructing this DownloadsSummaryData instance.
+   */
+  * _downloadsForSummary() {
+    if (this._downloads.length > 0) {
+      for (let i = this._numToExclude; i < this._downloads.length; ++i) {
+        yield this._downloads[i];
+      }
+    }
+  },
+
+  /**
+   * Computes aggregate values based on the current state of downloads.
+   */
+  _refreshProperties: function DSD_refreshProperties()
+  {
+    // Pre-load summary with default values.
+    let summary =
+      DownloadsCommon.summarizeDownloads(this._downloadsForSummary());
+
+    this._description = DownloadsCommon.strings
+                                       .otherDownloads2(summary.numActive);
+    this._percentComplete = summary.percentComplete;
+
+    // If all downloads are paused, show the progress indicator as paused.
+    this._showingProgress = summary.numDownloading > 0 ||
+                            summary.numPaused > 0;
+
+    // Display the estimated time left, if present.
+    if (summary.rawTimeLeft == -1) {
+      // There are no downloads with a known time left.
+      this._lastRawTimeLeft = -1;
+      this._lastTimeLeft = -1;
+      this._details = "";
+    } else {
+      // Compute the new time left only if state actually changed.
+      if (this._lastRawTimeLeft != summary.rawTimeLeft) {
+        this._lastRawTimeLeft = summary.rawTimeLeft;
+        this._lastTimeLeft = DownloadsCommon.smoothSeconds(summary.rawTimeLeft,
+                                                           this._lastTimeLeft);
+      }
+      [this._details] = DownloadUtils.getDownloadStatusNoRate(
+        summary.totalTransferred, summary.totalSize, summary.slowestSpeed,
+        this._lastTimeLeft);
+    }
+  }
+}